AN ABSTRACT OF THE THESIS OF
Edward Morgan Taylor
for the Master of Science in
(Name)
(Degree)
Geology
(Major)
`,Date thesis is presented
Title:
GEOLOGY OF THE CLARNO BASIN, MITCHELL QUADRANGLE,
OREGON
Abstract approved
(Major professor)
In the area surrounding Clarno, Oregon, pre-Cretaceous
nnetamorphics, Cretaceous marine sediments, and a varied
assemblage of Tertiary volcanic rocks are known. The
oldest exposures are of an homogeneously fine-grained,
mildly metamorphosed, limy shale to which the term "Muddy
Ranch phyllite" is applied. Non-metamorphosed, Cretaceous
marine shales and graywackes, approximately 1500 feet
thiclh, exist beneath the surface at Clarno. The beginning
of Tertiary vulcanism is recorded in the Clarno formation
of probable lower Eocene to lower Oligocene age. This is
succeeded unconformably by upper Oligocene to lower Miocene
tuffs and welded tuffs of the John Day formation. Middle
Miocene lavas of the Columbia River basalt formation were
the last major products of igneous activity in the area.
Unconsolidated Pleistocene and Recent deposits occur along
drainage channels.
The Clarno Basin was a depository of volcanic sediments from nearby centers of igneous activity throughout
Clarno time. Study of these rocks reveals the following
succession: The lower two-thirds of the Clarno formation
consists of a colorful series of volcanic conglomerates
and breccias indicating widespread conditions of mudflow.
While dominant in volume, these sediments record only
brief interruptions of a prevailing fine-grained lacustrine and floodplain deposition. Andesitic and basaltic
lavas of widely varying types were frequently spread over
the Basin near the mid-point of mudflow development.
This first stage of Clarno vulcanism was brought to a
close by the eruption of distinctive white and yellow
leucoandesites.
A time of quiescence is recorded in a widespread
sheet of very fine tuff which was deeply weathered as it
A flow of basaltic lava poured over this
accumulated.
surface, creating a lake in which a jungle-like flora
When the "fossil soil" had become nearly
200 feet thick at Clarno, a blanket of welded tuff reached
the Basin from a probable point of origin near' the Horse
Heaven amines. This was followed, after prolonged weatherina, by the eruption of pyroxene basalt which eventually
ivalled the inter inudflow lavas in thickness and distribution. As Clarno vulcaniscr, diminished, the terrane was
reduced to a low relief and thick, tuffaceous soil again
was preserved.
accumulated.
A recent and remarkable discovery of lower
Oligocene mammal remains was made in this horizon.
The
extravasation of an unusually gas-rich. andesite entombed
this surface beneath a resistant cap of ignimbrite. With
the appearance of another welded tuff sheet, probably
from the northeast, Clarno activity ceased.
A regional trend of northeast-southwest folds was
first developed during the late Cretaceous or Paleocene
and was accentuated during lower or middle Oligocene
time. This structural systc--v,, strongly influenced the
distribution of rocks formed within it. At the beginning
of the Tertiary, Cretaceous sediments were deeply eroded
from the anticlines, exposing older rocks. Clarno
volcanics were deposited unconfori;iably on this surface.
Post-Clarno uplift accelerated erosion of Clarno rocks
from the same anticlinal regions. Because structure also
determined topographic character, John Day tuffs were
A gentle warping o the
concentrated in the synclines.
older folds during Pliocene time involved the Columbia
Rive_'' Dasalts and is in part responsible for their
superior preservation in synclinal areas.
Present-day relief features in the Clarno Basin have
been in process of formation since the upper T`iiocene.
Two distinct periods of rejuvenation are recorded, one
during the upper Pliocene, another during the later
Pleistocene.
The Pliocene warping was not a necessary
factor in rejuvenation but may ''lave been contemporaneous,
increasing its effect in places, decreasing it in others.
APPROVED:
Professor of Geology
In Charge of Major
Chairman of Department of Geology
Chairman of School Graduate Committee
Dean of Graduate School
Date thesis is presented
Typed by Ruth
Chadwick.
TABLE OF CONTENTS
Page
INTRODUCTION
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THE PHYLLITE OF MUDDY RANCH
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Age and Stratigraphic Position
Petrography
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20
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Physiographic Expression
Petrogenesis . . . . . .
Discovery
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Lithology . .
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Age and Stratigraphic Position
Environment of Deposition . .
Structure . . . . . . . . . .
CLARNO FORMATION
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General Character
Clarno Intrusives
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Basalts and Andesitic Basalts
Andesites and Basaltic Andesites
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Clarno Lavas
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Inter-mudflow Lavas
Upper Clarno Lavas
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Crystallization . . . . . , . . . . .
Sequence of Eruption . . . . . . . . . . .
Clarno Volcanic Conglomerates and Breccias
Clarno Tuffs . . . . . . . . . . . . . . .
Clarno Welded Tuffs
JOHN DAY FORMATION
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Age
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Structure
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Occurrence and Definition
Lithol ogy . . . . . . . .
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Tuffs .
Welded Tuffs
Thickness . . . .
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6
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13
13
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Structural Relationships
CRETACEOUS MARINE SEDIMENTS
1
Environment of Deposition
117
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128
129
Page
COLUMBIA RIVER BASALT FORMATION
Definition
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Thickness
Structure
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Physiographic Expression
Lithology . . . . . . .
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132
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135
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135
137
137
PLEISTOCENE AND RECENT DEPOSITS
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139
GEOMORPHOLOGY
144
Age
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Origin
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STRUCTURAL GEOLOGY
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154
HISTORICAL SUMMARY
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167
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169
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Phys i ogra phy
Process . .
Stage . . .
NOTES OF ECONOMIC INTEREST
BIBLIOGRAPHY
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1124
159
LIST OF ILLUSTRATIONS
Pa g e
PLATES
1.
2.
Index Map Showing Location of Clarno
Basin
2
Correlation Chart for Central and North
Central Oregon
5
TABLES
1.
2.
3.
4.
5.
6.
8.
9.
Estimated Percentage Volumetric Modes
of 6 Samples of Muddy Ranch Phyllite
8
Generalized Succession of Clarno Rocks
in the Vicinity of Clarno, Oregon
9
Percentage Volumetric Modes of Clarno
Intrusive Basalts and Andesitic Basalts
30
Percentage Volumetric Modes of Clarno
Intrusive Andesites and Basaltic Andesites
31
Percentage Volumetric Modes of Clarno
Inter-mudflow Lavas
Percentage Volumetric Modes of Upper
Clarno Lavas
63, 64
69
Percentage Volumetric Modes of Clarno
Ignimbrite
l08
Percentage Volumetric Modes of Clarno
Welded Tuffs
116
Percentage Volumetric Modes of John Day
Welded Tuffs
122
FIGURES
1.
2.
Weathered, high-angle slope of Muddy Ranch
phyllite.
12
Basalt dike near Muddy Ranch.
34
FIGURES (Cont.)
Page
3.
Basalt plug, sec. 26, T. 8 S., R. 19 E.
35
4.
Arrested resorption of quartz in basalt.
Photomicrograph.
38
5.
Black Rock intrusive.
40
6.
Eagle Canyon intrusive.
44
7.
Dry Creek intrusive.
50
8.
Andesite dike, sec. 35, T. 7 S., R. 20 E.
55
9.
Vermicular embaymnents in quartz.
Photomicrograph.
57
Heulandite replacements in plagioclase
phenocrysts.
Photomicrograph.
77
11.
The "Palisades" on Pine Creek.
82
12.
Clarno mudflow.
86
13.
The "Nut Beds"
92
14.
The "Mammal Beds"
97
15.
Clarno ignimbrite at Clarno Pass.
104
16.
Clarno ignimbrite, lower zone.
Photomicrograph.
107
Clarno ignimbrite.
plain light.
Photomicrograph,
log
Clarno ignimbrite.
crossed nicols.
Photomicrograph,
10.
17.
18.
19.
Clarno ignimbrite segregate.
graph.
110
Photomicro113
20.
Slumped John Day tuff.
126
21.
Lower red John Day tuff.
127
22.
Pleistocene stone rings and nets.
Areal photograph.
141
Page
FIGURES (Cont.)
23.
Clarno mudflow,
sec. 5, T. 7 S.,
155
R. 19 E.
24.
Columbia
Mountain.
River basalts of Iron
157
ACKNOWLEDGEN .NTS
Indispensable assistance in manuscript preparation,
fieldwork, and laboratory studies was given by the
author's major professor, Dr. W. D. Wilkinson.
Greatly
appreciated was the kindness of Mr. and Mrs. A. W.
Hancock and others of the staff of the Portland Museum
of Science and Industry Youth Camp at Clarno.
Dr. Ira S.
Allison contributed much in editing the manuscript.
The
author is grateful to his wife, Beverley, for her help
in typing and in the preparation of thin sections.
GEOLOGY OF THE CLARNO BASIN,
MITCHELL QUADRANGLE, OREGON
INTRODUCTION
The name "Clarno Basin" is widely used in reference
to the area surrounding Clarno, Oregon, located on the
John Day rive= in the northwest quarter of the Mitchell
quadrangle.
Near the junction of the John Day and its
tributary, Pine Creek, a broad lowland of mild relief
partially surrounded by highlands of lava has been developed on soft tuffs.
This topographic feature is re-
sponsible for the term "Clarno Basin."
In the author's
usage, it will refer also to a Lower Tertiary basin of
sedimentation.
Location
The author has mapped and studied the geology contained in townships 7 and 8 south, ranges 19 and 20 east,
bounded approximately by north latitudes 45° 00' and 44°
49', and west longitudes 1200 30' and 120° 15', a total
of 151 square miles.
Wheeler Counties.
It includes parts of Wasco and
(See index map, plate I.)
Accessibility
The Fossil-Antelope road along Pine Creek (State
Route 218) bisects the area and is passable throughout
the year.
Other roads, while numerous, require favorable
weather and appropriate conveyance.
SALEM
S
CORVALLIS
EUGENE
0
PLATE I.
• BEND
RE GO
N
INDEX MAP SHOWING LOCATION OF CLARNO BASIN
r\)
3
Climate and Drainage
The general semi-arid climate of central Oregon is
influenced at Clarno by local conditions in such a way as
to increase, during the summer months, the day and night
temperature by several degrees, relative to surrounding
areas.
Of sixteen major tributaries, only two maintain
year-round flow, and even the John Day river has been
known to dry up during the month of August.
No quantita-
tive data from Clarno are available.
Relief
The highest and lowest elevations are 4230 feet on
the northeastern highlands and 1200 feet on the northern
boundary at the John Day river.
Vegetation
Sage and juniper, with small stands of pine in
favorable locations, are the conspicuous plants.
Previous Work
Geological literature dealing with the Clarno Basin
is very limited.
It includes paleobotanical notes by
Scott (35), a report by Stirton (39) of a vertebrate
find within the Clarno formation, petrographic descrip-
tions by Calkins (6), and a small structural map done by
Mackay (25) in 1938.
The best published geological map
4
to date was by Hodge in 1941 (20), but it is of a regional
reconnaissance nature.
Field and Laboratory Methods
Geologic mapping was done in 15 weeks during the
summers of 1957 and 1958.
Overlapping areal photographs
(contract flown 1951) and enlarged base maps of the United
States Geological Survey's 1926 edition of the Mitchell,
Oregon, topographic sheet were used.
In addition, the
author had 13 weeks field experience in the southern part
of the quadrangle.
An attempt is made, therefore, to
place the rocks at Clarno into a regional stratigraphic
and structural development involving both areas.
Laboratory investigations were carried on during the
school year 1958-1959.
Approximately 125 thin sections
were prepared and studied.
All modal determinations of
igneous rocks were made with a Wentworth recording
micrometer and mechanical stage.
In order to separate
Clarno rocks according to field relationships, igneous
classifications are those of Williams (46, p. 43).
General Stratigraphy
Three Tertiary volcanic formations, underlain by
Mesozoic marine sediments and metamorphic rocks of unknown age, occur in the Clarno Basin.
Their relationship
to other central Oregon rock units is summarized in
Plate 2.
UPPER
JOHN DAY
VALLEY
CLARNO
BASIN
after Coleman,
Recent and
Upper Pleistocene
Recent Alluvium
terrace
P/io-Pleistocene
deposits
DESCHUTES
UMATILLA
PLATEAU
after Cock?on,
Alluvium
\\\\\\\\Q.\\\\
COLUMBIA
RIVER
GORGE
offer Cockron,
Alluvium
Alluvium
\\\\\\\\\\\\\\ \.\\\\\\\\\\\\
Portland
sands & grovels
\\":5.1
g lociol grovel
Mount Hood
Coscan
Madras fm..
\\\\\\.\\.\.\\
\\\\\\\\\\\\\\ \\\\ \\\\`w \\\\\\\\\\\
boat
\\\\\\\\.
\r\
\\\\\'. \\\\\\ \\\\ .
:.=.%I
Pliocene
\\\.1
Rattlesnake
Columbia
Miocene
Riv
*k
C.
Imi
fm.
ve r b4s It\\
Upper & Middle John Day fm.
O//go-Miocene
John Day fm.
C
I
I
I
\ \\\\\\\\\\\\\
f IC
Dolles fm.
fm.
I
Colum i#f River basalt
Eagle Creek fm.
11 1 l i
I I
1
1
i
1
I
1
b'a R'v r s I
Colu gj2
Upper John Day fm.
Middle John Day fm.
%%
Lower John Ddy fm.
\\\\\\\\\\\\\
-'\\\\\\\\''\\ --'
I
TrruTTiflht 1 11
11
ClarnO fm.
Eocene
fm.
Lower John Day fm.
\\\\\\\\\\\\\\
-_ - - - - -
Oligocene
Troutdale
Rhododendron
Shutter fm,
Goble volcanic
series
Clorno
I
fm.
I
I
\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\
.
'
I
conglomerates
Cretaceous
sandstones, shales
Pre Cretaceous
\\\ \\ \ \\\\ \\\\\\\\\\\\\\
Muddy Ratich phyllite
PLATE 2.
CORRELATION
metosediments
CHART
FOR
CENTRAL AND
NORTH
CENTRAL OREGON
'
6
THE PHYLLITE OF MUDDY RANCH
"Muddy Ranch phyllite" is suggested as a fitting
name for the metamorphic rocks at the junction of Muddy
and Currant creeks in the southwest corner of the mapped
area.
They have a total areal distribution of approxi-
mately two and a quarter square miles, sixty per cent of
which is within the area of this investigation.
Age and Stratigraphic Position
The Muddy Ranch phyllite is the oldest rock known
in the Clarno Basin.
Merriam (28, p. 280) in 1901, wrote:
"0n several occasions, as parties have been passing
through the region, search has been made for fossils, but
so far no traces of them have been found.
Judging from
the appearance of this formation, it is older than the
Knoxville shales."
At the surface they are unconformably
overlain by early Tertiary volcanics.
No Cretaceous
rocks crop out in this area, but Cretaceous strata more
than 1500 feet thick have been found in deep wells, five
and one-half miles to the north.
As these rocks are un-
metamorphosed, the underlying phyllite must be older.
Because fossils are unknown at Muddy Ranch, a more
accurate age determination is not possible at this time.
The nearest fossiliferous, pre-Cretaceous rocks are
on the flanks of Tony Butte, south sixty degrees east of
7
Muddy Ranch and twenty-four miles away.
described by Bowers ().I.).
They have been
At that locality the writer has
observed marble, brecciated limestone, phyllite, sandstone, quartzite, conglomerate, serpentine, and altered
lava, all metamorphosed to varying degrees.
Certain
poorly preserved fossils, including brachiopods, pelecyopods, gastropods, crinoid stems, belemnoid rostra, and
questionable fusulinids, suggest that the Tony Butte
rm,etasediments range in age from Upper Paleozoic to Lower
However, lithologic correlation between the
Mesozoic.
variety of rocks at Tony Butte and the monotonous
sequence at Muddy Ranch is hazardous.
Petrography
The Muddy Ranch phyllite is made up of four rock
They are described as follows:
types.
Homogeneous Phyllite.
1.
Homogeneous phyllite (that portion of the outcrop
without bedding) is the most common.
Field specimens
appear dense, black, and hard when fresh, and coarse-
gained, light-brown to silver-gray, and friable when
decomposed.
to the
rock
A fine, crystalloblastic texture is imparted
by xenoblastic grains of quartz.
Several
modal analyses of selected phyllite samples are given in
Table 1.
The significant features of the constituent
minerals are as follows:
8
TABLE 1
Estimated Percentage Volumetric
Modes of 6 Samples of Muddy Ranch Phyllite
Sample Number
Constituent
Quartz
Calcite
Sericite
Muscovite
Magnetite
Hematite
Leucoxene
Plagioclase
Biotite
Chlorite
Epidote
Tourmaline
Apatite
Unidentified
argillaceous dust
T Trace:
No.
102
97
107
98
101
g0
102
97
107
98
101
90
58
43
28
50
67
82
68
-
3
-
6
18
5
2
1
23
5
3
1
1
2
T
2
3
4
4
1
1
2
2
24
11
-
23
5
-
T
T
-
-
1
T
-
1
-
2
2
1
T
-
-
T
-
-
-
-
T
T
T
T
T
-
T
-
T
-
-
-
7
22
2
T
4
-
T
26
-
-
-
less than 1%
Explanation
Inter-carbonate layer of argillaceous phyllite.
Carbonate layer in phyllite.
Homogeneous phyllite, fine-grained.
Homogeneous phyllite, much weathered.
Homogeneous phyllite, coarse-grained.
Homogeneous phyllite from quarry; unweathered.
Quartz.
quartz.
About sixty per cent of the phyllite is
It occurs both as porphyroblasts and matrix.
The fine-grained fraction is approximately 0.01 mm. in
size or smaller, and the coarse grains are 0.05 mm. or
larger.
The coarse to fine ratio averages 0.01.
The
large grains are angular to subrounded and "float"
separately in the fine matrix.
A sutured type of inter-
locking margins is typical of the finer particles.
A
distinct preferred orientation of the matrix grains
according to their C-axes is evident in most samples.
See Bedded Phyllite, page 10.
Calcite.
Muscovite.
Muscovite and its fine-grained form,
sericite, have a finely-shredded appearance and are found
between the quartz grains as long, thin streamers parallel
to the preferred orientation of the quartz.
The larger
muscovite laths attain a length of 0.1 mm. and are evenly
distributed.
Porphyroblastic texture is suggested by the
occurrence of muscovite and sericite, as well as by the
quartz.
Magnetite, Hematite, and Leucoxene.
Magnetite and
occasionally leucoxene were found as scattered, opaque
grains, about 0.05 mm. in diameter in all samples examined.
Magnetite is replaced by hematite in some weathered specimens, coloring them a dull brown.
The leucoxene is prob-
ably a secondary alteration of titaniferous iron oxides.
10
Plagioclase.
The rarity and small size of the
feldspar grains (1.03 - 0.05 mm.) render their identification difficult.
Several grains in sample 101 were
identified as albite.
Biotite and Chlorite.
Biotite and chlorite tend to
occur together in small amounts.
deeply colored.
The biotite is not
The chlorite and some magnetite may be
products of alteration from biotite.
Epidote, Tourmaline, and Apatite.
These minerals
occur sparingly and sporadically throughout the phyllite
as minute grains which are seldom larger than 0.03 millimeters.
The epidote and tourmaline are nearly always
xenoblastic, but apatite is idioblastic.
Unidentifiable "Dust".
An extremely fine-grained
fraction is present in every specimen, sometimes in large
It occurs as a fine dust within and between
amounts.
larger mineral grains.
It is probably argillaceous in
character.
2.
Bedded Phyllite.
Some of the examined phyllite specimens contain as
much as thirty per cent calcium carbonate in large grains
and micro-veins.
They are easily recognized in the field
by their solution-pitted surfaces and are invariably
found in layers, a few inches to several feet thick.
Be-
tween these high carbonate layers, the phyllite is similar
11
to the more common homogeneous type but lacks preferred
orientation.
3.
Cataclastic Rocks.
Adjacent to a small basaltic dike of section 31,
T. 8 S., R. 19 E., a zone of breccia is irregularly
exposed within strongly contorted phyllite.
The rock is
made up of a mosaic of angular fragments of phyllite,
one to three centimeters in diameter, which are cemented
by hematitic iron oxides.
The interstices are filled
with smaller fragments, or, in the event of extreme
granulation, individual grains of quartz from the broken
phyllite.
Some of the large fragments display an unusually
strong internal preferred orientation.
They may have been
brought up from an area of higher metamorphic intensity
by the intrusive.
4.
Quartz veins.
Randomly disposed veins of iron-stained quartz, a
few inches to three feet thick, are common throughout
the phyllite.
They are composed of firmly intergrown
quartz grains averaging 1 ram. long with the long direction
perpendicular to the vein wall.
Zones of micro-fractures
contain broken fragments of quartz enclosed in vein
calcite.
They seldom display slickensides or other
ternal evidence of rupture.
ex-
Fig. 1
Weathered, high-angle slope of
Note
Muddy Ranch phyllite.
small quartz veins transverse
to schistosity.
13
Structural Relationships
The two main structural features of the phyllite,
bedding and schistosity, are mutually exclusive, which
confuses the relationship between them.
This is probably
because bedding was obliterated during the development
of schistose structure.
The bedding is recognized by
layers of differing composition; grain size is nearly
constant and relatively unimportant.
Schistosity is shown
by its tendency to fracture in planes which include the
direction of preferred orientation of constituent particles.
Most of the areas where bedding is observable
display a high angle of dip approximately 50 degrees to
the southeast.
The exposed thickness of the Muddy Ranch
phyllite, on this basis, is about 5000 feet.
Minor
flexures and small but numerous faults are common throughout the rock.
Physiographic Expression
Outcrops of the phyllite are characterized by smooth,
rounded hills with steep slopes.
They are the result of a
higher resistance to chemical weathering than to physical
disintegration.
The fresh rock is black and hard, but
fractures with ease.
It breaks into small, angular
''pencils" and becomes fibrous.
A thin mantle of these
fragments is able to maintain an angle of repose of 35
14
degrees or more (see Fig. 1).
Eventually they weather to
a silver-gray, soft powder and are removed.
Petrogenesis
1.
Nature and depositional environment of the parent
rock.
The parent rocks from which the phyllites were derived were fine-grained sediments.
They could have formed
in a fresh-water environment, but the well-developed
bedding (where preserved), the indications of limestone
accumulation, the fineness and constancy of grain size,
the lack of high oxidation, and the similarity to some
of the known metamorphosed marine sediments at Tony Butte
suggest that the rock was probably deposited under marine
conditions.
2.
Mineralogical changes during metamorphism.
Petrographic examination shows that nearly all of
the minerals of the original sediment have been adjusted
to higher temperatures and pressures than those under
which they were deposited.
Calcite recrystallized into
relatively large grains either evenly dispersed through
the rock or segregated into a multitude of micro-veins.
The micas, tourmaline, and apatite were probably all
recrystallized and possibly reconstituted from the
argillaceous fraction of the shale.
Soda feldspar and
15
epidote were probably formed from plagioclase.
The
elements Al, Fe, Ca, Mg, Na, and K were probably present
as hydrous and anhydrous silicates.
Minor amounts of Ti,
P, F, and B were also indigenous, as would be expected
from known shale composition.
The fine, unidentifiable
dust which is found throughout the phyllite may represent
the only unchanged remnant of the original sediment.
The porphyroblastic and oriented texture displayed
by the quartz grains indicates that the minute particles
of the original shale were recrystallized, becoming fewer
in number and larger in size.
At closely spaced points
through the mass, conditions either favored the growth of
relatively coarser grains, or the original sediment was
inequigranular.
exudation veins.
The quartz veins in the phyllite may be
The silica was probably derived from the
phyllite itself, being dissolved by the fluids in the rock
and precipitated in zones of reduced pressure.
3.
Structural changes during metamorphism.
After deposition, the sediments were deeply buried
and brought into regions of elevated temperature.
During
this period, recrystallization progressed to the point of
complete crystallographic rearrangement of a majority of
the constituent minerals.
Under the influence of stress,
preferred orientation developed and became the dominant
structural feature of the phyllite.
16
4.
Intensity of metamorphism.
The Muddy Ranch phyllite is a product of very lowgrade regional metamorphism of quartz-rich, high carbonate,
pelitic shales.
It is to be placed in the greenschist
facies of Eskola, in the biotite zone of Barrow and Tilley,
and in the epi-depth zone of Grubenmann and Niggli.
The
phyllite is characterized by low temperature hydrous
silicates and a lack of garnets, amphiboles, or pyroxenes.
The common and intimate association of magnetite and
chlorite suggests the former presence of biotite.
Where
biotite exists, it is invariably light-colored.
It seems likely that increasing intensity of meta-
morphism would bring about a progressive reduction in the
amount of ultrafine-grained pelitic material and a corresponding increase in micaceous and certain other authigenic
minerals.
Preferred orientation should become more pro-
nounced, as should the content of biotite.
However,
measurements of the constituents of the phyllite do not
conform to this expected pattern.
The implication is that
the original sediment was already variable in composition
and grain size.
The presence of carbon dioxide might have
had a strong influence on the rate of recrystallization.
Moreover, full chemical and structural equilibrium is
commonly not reached in the lower grades of metamorphism.
17
CRETACEOUS MARINE SEDIMENTS
Discovery
A search for oil has shown that marine sediments
exist in the subsurface of the Clarno Basin.
In the
summer of 1957, a well was drilled by the Oregon Petroleum
Corporation in the northwest corner of SWu, SW-1, sec. 26,
T. 7 S., R. 19 E.
Drill cuttings were sampled at ten-
foot intervals, and a complete series was submitted to
the State Department of Geology and Mineral Industries.
The samples will be available for public inspection in
August, 1959.
The writer was allowed to examine cuttings
at the well site.
The drill first penetrated black shale
2400 feet below the surface.
A resistant layer of coarse
sandstone having a calcareous cement and a greenish cast
was encountered from 4100 to 4170 feet.
Drilling was
abandoned at a depth of 4250 feet while still in black
shale.
In 1936 a well was drilled by the Clarno Oil Company
to a depth of 4500 feet in the northwest corner of SE*.
SE;, sec. 34, T. 7 S., R. 19 E.
electrically and lithologically.
This well was logged
An interpretation of
the electric log is cited by Mackay (25, p. 7).
A
driller's record of the lithology from 300 to 4285 feet
has been reviewed by this writer.
Both sources of
18
information lack accuracy and objectivity but establish a
continental-marine transition at about the 2020-foot level.
Samples from this well are the basis of the rock descriptions that follow.
Lithology
1.
Sandstone
Cores of graywacke, recovered from the 1936
borehole,
probably represent the horizon of sandstone discovered in
the well of 1957.
They are light olive gray and are
The rock is composed
variegated with carbonaceous matter.
of rounded to subrounded grains of quartzite, 0.05 - 0.3
mm. in size, angular fragments of feldspar and quartz
(0.2 - 0.3 mm.), rounded grains of altered lavas (0.1 0.5 mm.), and opaque, intergranular, argillaceous dust
It is poorly cement-
(probably clay and organic material).
ed and requires artificial induration in preparing thin
sections.
An analysis is given below:
Per cent
Constituent
Quartz and Quartzite
Basic lava . . . . .
Felsic lava
.
.
Plagioclase . .
Potash feldspar
Calcite . . . .
.
.
.
.
.
.
.
58
7
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
3
2
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
4
22
.
.
.
.
.
.
T
.
Carbonaceous matter
.
.
.
.
.
.
.
Intergranular detritus
Apatite
.
.
.
.
.
.
.
2
19
Per cent
Constituent
Zircon
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Tie to s ed iment
.
.
.
.
Muscovite
Biotite
.
.
Chalcedony
.
.
T
T
T
T
T
Many of the quartz fragments are strained and show inclusions of apatite.
Most of the plagioclase is andesine.
The carbonaceous fraction is largely plant matter.
Grains
of phyllite are very rare, and none resembles the phyllite
from Muddy Ranch.
2.
Shale and siltstone
A majority of the marine strata encountered in the
wells were black calcareous shales and siltstones.
They
are composed of quartz particles (143%), cemented by
calcite (45%) and finely disseminated argillaceous matter
(12).
The grains range from clay to coarse silt and
display angular to rounded outlines.
sometimes occur.
Granules of pyrite
The shales are extensively fractured
and show slickenside surfaces.
Some of the fractures
contain vein-fillings in which outer zones of calcite
envelop an inner zone of equigranular fine-grained (less
than 0.01 mm.) quartz.
Twenty-two feet of three-inch
well cores were examined with a handlens; no fossils were
seen.
20
Age and Stratigraphic Position
The marine sediments discovered in the Clarno wells
are correlatives of exposed Cretaceous rocks in the
vicinity of Mitchell, 24 miles to the southeast.
Several
thousand feet of shales, graywackes, and overlying conglomerates have been reported there (2, 4, 22, 27, 40).
The shales near Mitchell are known from fossil evidence
to be Lower Cretaceous; some of the higher members are
Upper Albian.
Few fossils have been found in the con-
glomerate units; they are assumed to be Upper Cretaceous.
By any practical standard, the shales and sandstones from
Mitchell and Clarno are lithologically identical.
At both
localities they are overlain unconformably by the Clarno
formation.
It is highly probable that Muddy Ranch phyllite
underlies the shales at Clarno just as Tony Butte metasediments underlie shales at Mitchell.
Environment of Deposition
Cretaceous sediments were deposited in the Clarno
area under a variety of conditions, all of them marine.
The calcareous shale and siltstone reflect an off-shore
environment of rapid but orderly, fine-grained deposition.
Each horizon of graywacke records a disturbance of the
source which intermittently "poured" floods of angular,
coarse-grained sediments into the sea and spread them
21
over its floor in sheets of unsorted sand, silt, and clay.
The Upper Cretaceous conglomerates near Mitchell display
many features characteristic of a chaotic form of deposition.
These conditions were probably also in effect at
Clarno, but post-Cretaceous erosion has removed all trace
of marine conglomerate.
An eastern source area is strongly
suggested by the isopach distribution of Cretaceous sediments of the Rocky Mountain and Interior States (31).
As
Gilluly (18, p. 573) has shown, eastern Oregon was a part
of a region of profound uplift which became intensified
during the Upper Cretaceous.
Structure
The minimum thickness of the Cretaceous sediments at
Clarno, as computed from the following data, is 153+ feet.
A crude layering of the fine micaceous fraction is evident
in every hand specimen.
Elongate constituents are aligned
parallel to these layers and reflect the original attitude
of the sediment.
Measurements of greatest inclination
from the horizontal, relative to the assumed vertical
direction of 13 well cores, varied from 19 to 45 degrees
and averaged 34 degrees.
As the majority of measurements
were close to the average, it is thought to represent the
over-all inclination of the sediments.
The faulted
surfaces evident in the core specimens are probably small
22
displacements caused by folding of incompetent shale.
This condition is common at Mitchell and does not seriously
affect measurements of thickness.
Due to the lack of controlled orientation of the well
cores and the doubtful value of lithologic correlations
between the two holes, the structure of the Cretaceous
sediments at Clarno must be inferred from regional trends.
In the Mitchell area, Late Tertiary erosion of a northeastsouthwest anticlinal structure has removed the Clarno
formation, exposing the Cretaceous strata below.
A
similar erosional and structural history transpired during
Upper Cretaceous or Paleocene time.
The thick upper con-
glomerate units were removed from the axial region, and
the shales were so eroded in places as to expose the underlying metasediments.
Clarno volcanics were deposited
unconformably on the resulting surface.
Thus, in the
Mitchell area, Clarno rocks may overlie pre-Cretaceous
metamorphics as well as large thicknesses of Cretaceous
shale, without any intervening conglomerates.
Similar
conditions exist at Clarno.
The Clarno area is situated on the western limb of
the most prominent structural trend in the quadrangle,
referred to by Hodge (20, p. 49) as the Hay Creek anticline.
This anticline can be traced in a N. 60 E.
direction for at least 100 miles.
It is separated from
23
the smaller "Mitchell anticline" by the "Sutton Mountain
syncline" of Bedford, McIntyre, and Swarbrick (2, 27, h0).
Although erosion of the ('3larno formation has exposed
scattered outcrops of pre-Cretaceous rocks throughout
its length, no strata of Cretaceous age have been reported
from within the boundaries of the Hay Creek anticline.
Post-Cretaceous, pre-Clarno uplift and erosion presumably
removed the Cretaceous strata from most of the structure.
The fact that 1500 feet of Cretaceous shale pinches
out between Clarno and Muddy Ranch may be explained by
appealing to an island of non-deposition in. Cretaceous
seas or as a manifestation of the erosional history outlined above.
The "island" would have shed coarse elastics
predominently composed of phyllite; these have not been
found.
The foregoing is the basis for certain structural
speculations concerning the subsurface Cretaceous shales
at Clarno:
1)
They were deformed and eroded prior to Tertiary
folding.
An upper sequence of conglomerates may
have been removed.
2)
They have a northwest dip of approximately 34
degrees.
3)
They may be expected to pinch out toward the
axis of the Hay Creek anticline to the east and
24
toward Muddy Ranch to the south.
4)
Their thickness may increase westward.
5)
Considering the distances involved in 3), their
total thickness at Clarno is probably not much
greater than the minimum value already given.
6)
They are underlain by Muddy Ranch phyllite.
25
CLARNO FORMATION
General Character
Definition
In 1901, J.
C. Merriam (29) gave the name "Clarno"
to a formation of "tuffs, ashes, and lavas ... resting
upon the Chico, near Mitchell, also showing typical
exposures at Clarno Ferry."
It is now known to be dis-
tributed over much of central Oregon.
Lithology
Clarno vulcanism, as seen in the Clarno Basin, was
highly explosive.
Vesicular lavas and welded tuffs were
interbedded with great accumulations of tuffaceous sediments.
Late deuteric alteration, a common feature of
most Clarno lavas, suggests a high content of volatiles.
The effusive rocks are of three main types:
basalts
composed of labradorite and pyroxene with varying amounts
of glass, andesites of several sorts that vary mainly in
their content of mafic minerals, and a peculiar leuco-
andesite of nearly pure andesine and iron oxide with
occasional hornblende.
A distinction is drawn between
light-colored basaltic andesites and dark-colored andesitic
basalts, both containing transitional labradorite-andesine
(Ab 40-60) and minerals common to Clarno andesites, for
26
example, hornblende, zircon, apatite, and unstable quartz.
The ground-
All igneous rocks observed were porphyritic.
mass ranges from the trachytic and pilotaxitic texture and
uniformly fine grain of most of the lavas to the felted
texture and wide range of grain size seen in most intrusives.
Age and Stratigraphic Position
Through long usage, the term "Clarno formation" now
embraces all central Oregon rocks found to lie strati-
graphically above the Cretaceous sediments and below the
John Day tuffs.
The time boundary at the bottom of the
Clarno is not known, and the upper lithologic boundary
is often in dispute.
Mid-Eocene ferns have been found in
Clarno tuffs on Branch Creek near Mitchell
(5).
Stirton
(39) described a Middle Eocene rhinoceros tooth taken
from Clarno red tuffs at Clarno.
Chaney (8) dated the
Clarno as Upper Eocene on the basis of fossil leaves.
Scott (35) compares Clarno nuts and fruits to those from
the London clay of upper Lower Eocene age.
The U.
S.
Geological Survey recognizes the Clarno formation as Lower
Oligocene and Upper Eocene (47).
Eo-Oligocene mammal
remains have recently been discovered in upper Clarno
tuffs near Clarno.
The Paleocene epoch has not been
recognized in central Oregon.
27
Structure
The attitude of Clarno rocks is difficult to determine and variable over short distances.
Their dip in the
Clarno Basin is to the northwest, but minor complications
arise, particularly in the western half of the area.
Well
cores suggest an angular unconformity of about 15 degrees
between Cretaceous sediments and Clarno volcanics at
Clarno.
At Mitchell, where direct measurement is possible,
the discordance from place to place varies from 0 to 18
degrees.
Estimates based on well data and structure
suggest a thickness of about 3200 feet for the Clarno
formation near Clarno.
Maximum exposed thickness in the
eastern part of the area is about 1500 feet.
Environment of Deposition
The Clarno formation, in the Clarno Basin and elsewhere, contains fossils of plants which grew in a humid,
subtropical environment.
It may be assumed that the
Pacific coastline was then near the modern Cascade Range
and that rainfall was plentiful. Animals were abundant,
but conditions of preservation were poor.
Thick mudflow
conglomerates and lacustrine deposits in the Basin were
derived in large part from the east and southeast where
they grade into volcanic breccias associated with centers
of eruption.
These facies variations are difficult to
28
interpret because erosion and deposition followed each
other intermittently in time and space.
Relief was
probably like that of present-day regions of active
terrestrial vulcanism; but as activity waned, the topography was reduced to low hills and broad plains.
Clarno
rocks were often deeply weathered.
Clarno Intrusives
Twenty-three plugs and dikes of porphyritic basalts
and andesites were mapped.
Others undoubtedly exist but
are difficult to identify.
A Clarno age is assumed for
all of these intrusives on the basis of their field relationships, their resemblance to surrounding Clarno
lavas, and the lack of similar rocks in earlier and later
formations of the area.
the intrusive groups.
Tables 3 and t . present modes of
Numbers in the text correspond to
those in the tables.
Basalts and Andesitic Basalts
1.
Basalt dikes near Muddy Ranch.
Near the center of section 31, T. 8 S., R. 19 E., on
the north side of the Muddy Ranch-Antelope road, two small
dikes of basalt display a notable joint pattern.
The
normal stresses of internal contraction were modified
during the last stages of crystallization by movement of
29
TABLE 2
Generalized Succession of Clarno
Rocks in the Vicinity of Clarno, Oregon
John Day tuffs
----------------- UNCONFORMITY----------------(11)
Clarno upper welded tuff
(10)
Clarno ignimbrite
(9)
Red and buff clay tuffs containing vertebrate fossils
(8)
Coarse and fine pyroxene basalts, andesitic
basalts, and interbedded volcanic breccias
(7)
Clarno lower welded tuff
(6)
Red, green, and buff clay tuffs with interbedded amygdaloidal basalt, tuffaceous lake
deposits
(5)
White
(4+)
Volcanic conglomerates and breccias of
mudflow origin
(3)
Highly variable andesitic and basaltic
(2)
Volcanic conglomerates and breccias of
mudflow origin
(1)
Not exposed at
to yellow leucoandesites
inter-mudflow lavas
Clarno,
probably mudflow
----------------- UNCONFORMITY----------------Cretaceous shales and sandstones
30
TABLE 3
Percentage Volumetric Modes of Clarno
Intrusive Basalts and Andesitic Basalts
Constituent
Andesine
Labro-andesine
Labradorite
Sodic Plagioclase
Augite
Diopside
Hornblende
Magnetite
Hematite
Chlorite
Quartz
Apatite
Calcite
Glass
Epidote
(1)
(2)
(3)
(4)
(5)
T
1
63
77
T
38
20
11
35
82
67
T
5
T
T
T
T
28
T
T
2
3
T
T
1
7
9
2
T
15
T
T
T
T
18
14
T
T = less than 1%
Explanation:
(1)
Muddy Ranch dike, sec. 31, T. 8 S., R. 19 E. (T-106)
(2)
Plug, sec. 26, T. 8 S., R. 19 E.
(T-71)
(3)
Plug, sec. 26, T. 7 S., R. 19 E.
(T-400)
(4)
Black Rock intrusive, sec. 25, T. 8 S., R. 19 E.
(T-149)
Dike north of lower Eagle
R. 19 E.
(T-145)
Canyon,
sec.
24,
T. 8 S.,
31
TABLE 4
Percentage Volumetric Modes of Clarno
Intrusive Andesites and Basaltic Andesites
Constituent
Andesine
Labro-andesine
Hornblende
Augite
Biotite
(1)
(2)
87
91
11
5
(4)
(5)
90
95
(6)
(7)
(8)
T?
92
72
T
70
T
T
Quartz
Magnetite
T
1
Hema tite
Limonite
T
T
T
3
2
T
15
1
T
T
T
T
T
T
62
6
1
1
1
T
T
T
T
T
T
16
T
T
T
Chlorite
Apatite
Zircon
Rutile
Leucoxene
Heulandite
Chalcedony
Calcite
T = less than
(3)
T
T
T
26
T
T
T
T
T
T
T
T
T
T
2
12
8
3
T
T
T
19
T
1%
Explanation:
Eagle Canyon intrusive, sec. 24, T. 8 S., R. 19 E.
(T-33)
(2)
Plug, sec. 36, T. 7 S., R. 20 E.
(T-138)
(3)
Plug, sec. 24, T. 8 S., R. 20 E.
(T-58)
(4)
Porcupine Butte plug, sec. 10, T. 8 S., R. 20 E.
(T-14)
(5)
Dry Creek plug, secs. 17 "U 20, T. 8 S., R. 19 E.
(T-8o)
sec. 3, T.
8 S., R. 20 E.
(T-57)
(6)
Pine Creek dike,
(7)
Plug, Rhoads Canyon, sec. 21, T. 8 S., R. 20 E. (T-13)
(8)
Clarno ignimbrite dike source, sec. 35, T. 7 S.,
R. 20 E.
(T-69)
32
unsolidified lava which was most effective in the central,
least consolidated portion of the dike.
This is inferred
from the fact that columns, in a horizontal position at
the dike margins, curve upward toward the interior, meeting in a plane parallel and central to the intrusive mass
(see Fig. 2).
These dikes are probably Clarno in age.
They dis-
cordantly intrude Muddy Ranch phyllite, producing contortion and brecciation.
They have not been metamorphosed.
No basalts of Cretaceous or John Day age are known in this
region.
The nearby Columbia River basalt flows are all
unlike these dikes in texture and composition.
Under the hand lens, an anastomosing pattern of long,
thin, subparallel "streamers" is visible.
Clarno basalts
and basaltic andesites often display this distinguishing
feature, while Columbia River basalts apparently do not.
Under the microscope, the "streamers" are seen to be
linear zones in which glass is concentrated.
The orienta-
tion of adjacent microlites shows that the last fluid
motion of the rock was one of differential movement along
these glassy zones.
Subsequent alteration stains the glass
and creates a directional weakness which strongly
influences later fracturing.
The plagioclase phenocrysts are normal and reverse
zoned from calcic andesine to sodic labradorite.
The rims
33
are slightly more sodic than the groundmass which is midlabradorite.
Pyroxene also occurs in two generations.
crysts of augite are larger than 1.0 mm.
Few pheno-
Evenly distribu-
ted, minute crystals of subhedral clino-pyroxene, probably
augite, make up about one third of the groundmass.
The dike margins are light-colored, finer-grained and
more glassy than the interior.
Partially resorbed
grains of quartz up to 0.55 mm. long are common near the
margins and were probably incorporated from the surrounding rocks.
The sequence of crystallization seems to have been
plagioclase and pyroxene phenocrysts, magnetite, plagioclase and pyroxene groundmass, followed by the solidification of glass in narrow zones between separate accretions of groundmass crystals.
2.
Basalt plug, section 26, T. 8 S., R. 19 E.
Near the center of the SE- , of the above section, a
large pluglike body of quartz-bearing basalt rises nearly
:-500 feet over the west bank of the John Day river.
Con-
tinuous, slightly curved columns extend from the base of
the outcrop nearly to the summit (see Fig. 3).
Clarno age is indicated by a flow of almost identical basalt adjacent to the plug and extending downstream
•
ii
•
,';
j:
?
I
3
Fig. 2
Basalt dike near Muddy Ranch.
Note upward convergence of
columns toward center.
___—
,
.
Fig. 3
Basalt plug (left center of picture)
near midpoint of SE-1, sec. 26, T. 8
S., R. 19 E.
36
and across the river for approximately one mile.
It is
intercalated with Clarno mudflow conglomerate.
This basalt intrusive is similar to those near Muddy
Ranch.
The same type of flow structure is seen under the
microscope, but in the absence of glass the corresponding
megascopic features are lacking.
Plagioclase phenocrysts are of two types:
1.
Large (up to 2.0 mm.), strongly zoned
crystals of calcic andesine.
Partial or entire
replacement by an aggregate of small crystals
of epidote demonstrates their instability.
They
strongly resemble phenocrysts in Clarno andesites.
2.
Smaller (up to 0.5 mm.), clear, poorly zoned
crystals of labradorite which seem to be stable.
Grains of quartz also occur and are surrounded and
embayed by (from the center, outward):
1.
A rim of clear sodic feldspar having a low
index of refraction relative to quartz.
The
glass, surrounding quartz in basalts, which has
been reported by Calkins (6, p. 135) and others,
was not seen here.
2.
A zone of small quartz particles still in
optical continuity with the core, more of the
same feldspar, and crystals of a pyroxene of the
37
diopside-hedenbergite series having a very high
index of refraction and a maximum extinction
angle of 242 degrees.
The pyroxene is oriented
and terminated as if it had grown toward the
cores as a second wave of reaction succeeding
the feldspar (see Fig. 4).
The points of origin
of the crystals describe a smooth and definite
boundary around the quartz grains.
The pyroxene
itself shows no effects of resorption.
3.
An outer, broad halo of green stain, pre-
sumably chlorite.
This and the characteristic
pattern of pyroxene often are the only remaining
traces of a completely resorbed quartz grain.
A fine groundmass of labradorite with magnetite,
clino-pyroxene, and traces of apatite constitutes 98 per
cent of the rock.
Chlorite and calcite occur as products
of groundmass alteration.
3.
Basalt plug, sec. 26, T. 7 S., R. 19 E.
In the SW-, NE* of the above section, a basalt in-
trusive forms the ridge between the head of Hancock
Canyon and the western slope of Indian Canyon.
completely surrounded by volcanic sediments.
It is
Columnar
jointing is crude but discernible in both vertical and
horizontal attitudes.
hid. 4
Arrested resorption of quartz in
basalt plus of Sec. 26, T. 8 S.,
R.
1
E.
Photomicrograph.
X, plain light.
39
The basalt is spheroidally weathered.
To obtain a
good petrographic sample it is necessary to reduce a large
block to a small, relatively fresh, spherical core.
The
most distinctive outcrop feature is the glassy luster
produced on the curved fracture surfaces.
Veins of calcite
and stilbite are common.
Megascopically, the rock is uniformly black and
without textural detail; phenocrysts are not visible.
Under the microscope a fine, pilotaxitic, intersertal
texture of labradorite microlites, minute crystals of
clino-pyroxene, and irregular patches of altered glass,
is seen.
Weakly-zoned plagioclase phenocrysts make up ten
per cent of the rock but attain a maximum size of only
0.25 mm.
Order of crystallization is probably not signifi-
cant because of rapid cooling; 90 per cent of the rock is
fine groundmass containing 18 per cent of glass.
4.
The Black Rock intrusive.
A fin-shaped plug of andesitic basalt, known as Black
Rock, stands in bold relief in the NEI, SEQ., sec. 25, T. 8
S., R. 19 E.
(see Fig. 5).
It is surrounded by lavas of
nearly identical composition but differs from them in its
coarse texture and in possessing an even gradation in size
of crystals.
The freshest hand specimen obtainable has the dull
gray cast of an altered rock.
It is very hard, dense, and
Fig. 5
Black Rock intrusive, sec. 25,
T. 8 S., R. 19 E. View of the
North-south
broad south face.
dimensions are relatively narrow.
41
without visible phenocrysts.
Weathering produces a soft,
reddish-brown surface.
Thin sections show abundant phenocrysts of transitional andesine-labradorite up to 0.3 mm. in size with a
fine groundmass of similar plagioclase.
However, no
definite boundary can be drawn between the two extremes.
Zoning is poorly developed.
The rock may once have con-
tained up to ten per cent hornblende.
Except trace
amounts, all that remain are pseudomorphous rims of
magnetite and chlorite.
altered phenocrysts.
Augite is present in small, un-
Particles of magnetite occur
interstitially and as inclusions in all major constituents.
Chlorite is of two unidentified types.
One, the most
abundant, is light-buff in reflected light and nearly
opaque in transmitted light.
It occurs in the hornblende
reaction rims and as scattered grains in the groundmass.
The other chlorite mineral is light green to yellow with
a fibrous, felt-like texture in transmitted light and
dark in reflected light.
It occurs as inclusions in the
larger plagioclase phenocrysts.
5.
Dike north of lower Eagle Canyon.
One-eighth mile south of the center of section 24,
T. 8 S., R. 19 E., a small, east-west dike of andesitic
basalt crops out.
It is ten to twenty feet wide and
about 300 feet in visible length.
An altered contact
42
zone, several inches thick, is poorly developed in
adjacent volcanic sediments.
Columnar jointing in the
dike is horizontal.
The hand specimen lacks distinctive features.
When
fresh, it is dark grayish brown with a greasy luster,
weathering to a dull tan.
Under strong magnification,
amygdaloidal fillings and occasional phenocrysts of
euhedral pyroxene and altered feldspar can be seen.
Microscopically, a very small number of plagioclase
phenocrysts, up to 1.0 mm. in size are set in a matrix
of 0.1 mm. andesine-labradorite laths and devitrified
glass.
No zoning is apparent.
In contrast to the nearby
Black Rock intrusive, only one relict crystal of hornblende was seen, augite phenocrysts are plentiful, and
the rock is almost devoid of magnetite.
Minute, irregular
vesicles constitute about ten per cent of the total
volume.
Nearly every one contains a single terminated
quartz crystal, which protrudes into the cavity from the
margin.
Covering this and filling the remaining space is
concentrically layered, grass-green chlorite.
Andesites and Basaltic Andesites
1.
Eagle Canyon intrusive.
The northern border of Eagle Canyon in section 24,
T. 8 S., R. 19 E. and section 19, T. 8 S., R. 20 E., has
43
been cut into an elongate east-west mass of intrusive
hornblende andesite.
It is slightly more than one-half
mile long and one-eighth mile wide.
High, spired cliffs
of white, yellow, and buff rock characterize the outcrop
(see Fig. 6).
No pattern of cooling fractures was noted
in the main mass, but a small, subsidiary dike to the
northeast contains horizontal columns.
Fault surfaces
of unknown displacement, in seemingly random orientation,
transgress the intrusive.
They contain large veins of
calcite.
Megascopically, phenocrysts of zoned plagioclase
up to 10 mm. in size and hornblende up to 4 mm. are seen
in a light-colored groundmass.
The larger phenocrysts
make up about 25 per cent of the rock.
generations are not apparent.
Definite crystal
In general, the larger the
feldspar crystal, the more calcic.
The smallest "ground-
mass" fraction is mid-andesine, and the largest, most
strongly zoned phenocrysts vary from mid-labradorite to
mid-andesine.
Zoning in the plagioclase phenocrysts is highly
variable and complex.
In attempting an analysis, certain
features of primary importance were noted:
1)
Continuous zoning.
In the following text, a plagioclase crystal
which varies in composition gradually without sharp
4,'
k.
Fig. 6
Eagle Canyon intrusive, Sec. 24,
T. 8 S., R. 19 E.
45
breaks, will be.referred to as "continuous normal"
as the direction of change
is calcic to sodic or sodic to calcic, respectively.
or "continuous
reverse",
Some crystals show "continuous
2)
oscillitory"
zoning.
Discontinuous zoning.
When the above conditions are interrupted by
abrupt
changes,
"discontinuous normal" or "discontin-
uous reverse'' zoning may result.
3)
Resorption and repair.
Well-defined
zones,
outlining crystal boundaries,
may "unconformably" succeed rounded, irregular cores,
displaying cycles of partial melting and regrowth.
Comparison of zoning in phenocrysts of favorable
orientation
growth
(normal to 010) brings out similarities in
patterns.
Most types begin with an unzoned core
of mid-labradorite which is usually one-eighth to oneAs many as fifty
sixteenth the diameter of the crystal.
unconformable layers may succeed this core, each with its
own set of discontinuous normal or reverse zones. There
is no over-all change in composition in this second midandesine stage. A relatively thick continuous normal
zone usually encloses the crystal. It has a composition
as calcic as the core but grades rapidly near the rim to
mid-andesine.
46
Occasionally, zoning is absent in alternate twin
bands of otherwise highly zoned crystals.
This condition
was observed in several sections cut normal to (010),
eliminating the possibility of accidental orientations
which may reduce the contrast between zones.
Reaction rims of magnetite and chlorite surround all
crystals of hornblende.
Minor amounts of quartz, augite,
apatite and zircon are present.
tion is apparent:
An order of crystalliza-
apatite and zircon followed by
hornblende and plagioclase phenocrysts; quartz, followed
by the groundmass and products of hornblende alteration.
2.
Hornblende andesite of sec. 36, T. 7 S., R. 20 E.
The easternmost projection of the south end of the
ridge in the above section was questionably mapped as an
intrusive plug of porphyritic hornblende andesite.
In
outcrop and thin-section features, it closely resembles
the much larger Eagle Canyon intrusive.
Less hornblende
and slightly smaller plagioclase phenocrysts are the main
differences.
3.
Basaltic andesite plug of sec. 24, T. 8 S., R.
20 E.
On the eastern border of the above section a rounded
plug of basaltic andesite, 3907 feet in elevation, is
situated amid outwardly sloping lavas and breccias of the
same appearance and composition.
47
In the field, the fresh rock is light gray, tinged
with minute spots of red.
It weathers to a dull brown.
Large phenocrysts of plagioclase up to 5 mm. in size are
visible.
Microscopically, the rock is relatively simple in
composition.
ment,
This is probably due to extensive replace-
Pseudomorphous hematite, showing the characteristic
outlines of hornblende, with traces of the hornblende
reaction corona still visible, and sodic labradorite,
partially replaced by heulandite, constitute 97 per cent.
Magnetite, found in the cores of the large clusters of
hematite, may have been the first pseudomorphous mineral.
The phenocrysts show complex patterns of discontinuous
normal and reverse zoning but range only from mid- to
sodic labradorite.
Zoning is absent in some twin laminae.
The groundmass is sodic labradorite.
Zoning and twinning
are present in the larger groundmass crystals.
An un-
usually large amount of apatite with traces of quartz and
zircon was noted.
A strong tendency to replace calcic zones and cores
is shown by a clear, anhedral mineral of low relief (see
Fig. 10).
Calkins (6, p. 129), in examining a "boulder
in the tuff beds of Clarno's Ferry", encountered this
phenomenon.
He writes:
"Their (the phenocrysts') altera-
tion, which is in general far advanced, is of an
48
interesting and unusual character.
The writer has observ-
ed nothing similar except in the Clarno rocks, and has seen
nothing in the literature that would apply to the present
case."
In a lengthy discussion, he concludes that the
replacement mineral is heulandite.
concurs.
The present writer
It has a birefringence close to .008 and an index
of refraction less than 1.51-. The character is positive.
Occasionally fine lines, presumably cleavage traces, are
present.
The axial plane is parallel to them.
The
characteristic replacement pattern, in which the heulandite
closely follows plagioclase zoning, is made visible in the
hand specimen by heating a polished surface with a blowpipe
until a white enamel of exfoliation appears.
Some water of
crystallization is driven off by the heating.
3a.
Plug north of Eagle Canyon intrusive.
Near the east central border of sec. 2L, T. 8 S.,
R. 19 E., a basaltic andesite plug forms the high point on
the ridge just north of the Eagle Canyon intrusive.
The
writer was unable to find any significant difference
between it and the plug of sec. 24, T. 8 S., R. 20 E.,
just described.
4.
Porcupine Butte intrusive.
Porcupine Butte in section 10, T. 8 S., R. 20 E.
and two narrow, east-west dikes in the southern part of
the adjoining section 11, are composed of a light tan
49
porphyritic andesite.
Phenocrysts of quartz and plagio-
clase up to 8 mm. in size are visible in the hand
specimen.
Microscopically, the rock is similar to the last
described plugs (sec. 24, T. 8 S., R. 20 E.)
in the
simplicity of its composition and in the high degree of
heulandite replacement.
The groundmass crystals are very
small (0.01 mm. or less) and could be identified only as
plagioclase.
Larger crystals, comprising 46 per cent of
the rock are discontinuously normal and reverse zoned from
mid-labradorite to calcic oligoclase.
Most phenocrysts
show only one cycle of resorption and repair.
zone is usually mid-andesine.
The outer
Heulandite replacement is
more pronounced in the groundmass than in the phenocrysts.
Strongly resorbed quartz grains and traces of hornblende,
magnetite, chlorite, apatite, and zircon are present.
5.
Dry Creek leucoandesite intrusive.
On the eastern end of the border between sections
17 and 20, T. 8 S., R. 19 E., a large homogeneous andesite
mass is surrounded in part by tall yellow and white cliffs
(see Fig. 7).
It is interpreted as the intrusive source
of nearly identical lavas which form the canyon walls of
lower Dry Creek.
Near its southern margin, a small
outcrop of lower Clarno sediments, containing pebbles of
Fig.
T
Di-y Creel'. intrusive, Sec. 20,
T. 8 S. , R. 19 E.
51
the type found in Cretaceous conglomerates elsewhere in
the quadrangle, has been sharply displaced.
A hand specimen of the intrusive rock can only be
classed as a slightly porphyritic felsite.
It may be
white or tan, changing to gray or black on weathered
surfaces.
The Dry Creek intrusive is almost monomineralic.
It is 90 to 96 per cent mid-andesine.
Small, variable
amounts of chlorite suggest the former presence of
pyriboles.
Traces of magnetite, apatite, zircon, and
rutile were observed in thin section.
At least three
per cent of the andesine has been replaced by heulandite.
Phenocrysts ranging in size from 0.3 to 1 mm. make up
about 16 per cent of the rock and are highly zoned.
A
pattern of one or two discontinuous zone-groups of sodic
andesine grading normally into a core of calcic andesine
is common.
Discontinuous reverse zones on the margins
have the same composition as the cores.
Heulandite re-
placements occur along cleavage traces and within calcic
zones of the phenocrysts as well as in long, thin,
optically continuous veins in the groundroass.
6.
Pine Creek dike.
In the NE-4.,
sec. 3, T. 8 S., R. 20 E., a dike of
basaltic andesite, showing crude horizontal jointing,
rises from the north embankment of the Pine Creek road
52
and passes northeastward into a large plug-like intrusion
in sec. 34, T. 7 S., R. 20 E.-
In the opposite direction,
it reappears one-half mile. downstream on the south side of
Pine Creek.
Total exposed length is one and one-eighth
miles.
In the field, the rock is light tan with spots of
greenish-yellow.
It is not visibly porphyritic.
Under the microscope, the groundmass is pilotaxitic
and contains irregular cavities.
It is composed of 0.05 -
0.3 mm. crystals of calcic andesine intimately mixed with
fine, green to yellowish-brown chlorite.
larger cavities are filled with chlorite.
Some of the
They are pene-
trated by inwardly-growing needle-like crystals of zeolite
(?) which are firmly rooted in the groundmass.
Pheno-
crysts of mid-andesine, up to 1 mm. in length, often
display several successive chlorite bands which closely
follow the zonation.
They were probably produced as an
alteration product of hornblende during the formation of
the phenocrysts.
in the rock.
A trace of hornblende may still be seen
Apatite, quartz, magnetite, hematite, and
leucoxene are also present.
7.
Quartz andesite plug of Rhoads Canyon.
In the west center of sec. 21, T. 8 S., R. 20 E.,
a white domical hill rises 150 feet above surrounding
Clarno tuffs.
Contact relations are poorly exposed, but
53
intrusive character is inferred from its unique lithology,
replacement features, and high degree of similarity to
dacite plugs in the Mitchell area.
The rock is not
strictly a dacite in Williams' classification, but rather
a quartz andesite.
Hand specimens are white to yellow and chalky in
appearance but difficult to break with the hammer. Soft,
yellow, rectangular areas, 1 to 8 trim.
per cent of the rock.
long comprise 19
They resemble much-altered plagio-
clase phenocrysts.
Under the microscope, the rock is 62 per cent quartz
which occurs as minute groundmass particles with sutured
margins.
A network of opaline silica and chalcedony
veinlets traverses the rock, sometimes passing imperceptibly into large pseudomorphs of chalcedony after plagioclase
phenocrysts.
Part of the original zoning and twinning
pattern is often preserved.
Small, lath-shaped pseudo-
morphs of the same type are common in the groundmass. Only
traces of feldspar remain in the rock.
A fine "dust" of
limonite permeates the groundmass and occurs with
chalcedony as a replacement of plagioclase phenocrysts.
Grains of magnetite surrounded by hematite are common.
Other minor constituents include black dendritic markings
(manganese oxide?) in chalcedony, calcite grains, and
apatite.
54
8.
Dike source of Clarno ignimbrite.
In the east-central part of sec. 35, T. 7 S., R. 20
E., and in the western and northwestern parts of sec. 1,
T. 8 S., R. 20 E,, there are three northeast-southwest
dikes which appear to be the intrusive source of the
Clarno ignimbrite (see Fig. 8).
The north dike displays
vertical striations of emplacement similar to those on
the plug dome of Mount Lassen as described by Williams
(45, p. 319).
Each of the southern pair contains crude
horizontal jointing.
The fresh rock varies from light gray to white, but
weathers to reds and browns.
Phenocrysts of quartz,
biotite, and clear feldspar are abundant but seldom
exceed 2 mgr,.
in size.
The groundmass is dense and glassy
with a splintery fracture.
Petrographically, the dikes are not easily distin-
guished one from another except for a slightly higher
content of quartz in the northern one.
Their groundmass
is composed of unoriented laths and anhedral crystals of
andesine, 0.01 mm. or less in size.
Spherulites, 0.01
to 0.1 mm., are scattered throughout the groundmass and
appear to be intergrowths of quartz and feldspar.
Pheno-
crysts of mid-andesine, biotite, and quartz comprise 12
per cent of the rock.
The plagioclase often shows dis-
continuous normal zoning.
Broad plates of deeply-colored
Fig. 8
Andesite dike in east central
Sec. 35, T. 7 S., R. 20 E.
Probable source of Clarno ignimNote vertical emplacement
brite.
striations.
56
biotite, up to 1.5 mm. in length, are partly replaced
along their longitudinal margins by minute spherulites.
Rounded crystals of quartz, up to 3 tam., display vermicu-
lar embayments in which spherulites often enclose a central
filling of heulandite (see Fig. 9).
A thin band of
chlorite is sometimes developed between them.
Irregular
clusters of heulandite surrounded by spherulites are
common in the groundmass and mark the sites of resorbed
quartz phenocrysts.
Although no contact is seen between these dikes and
the Clarno ignimbrite, several observations suggest a
common time and place of origin.
Thickness of the ignim-
bite, where full sections are preserved, decreases with
distance from the dikes.
The direction of vesicle
elongation in the ignimbrite was determined in several
localities.
Most of the measurements were within twenty
degrees of the compass bearing to the inferred intrusive
source.
The similarity between phenocrysts of both units
is striking.
The composition of the ignimbrite glassy
zone, based on index of refraction, is that of an andesite.
Moreover, no other rock was encountered in the area, either
in place or transported, which resembled the dikes in
character or make-up.
-.
-.
Fig. 9
'.
F
Photomicrograph of dike in Fig. 8
showing vermicular embayments of
groundmass plagioclase and chlorite
in quartz. Mineral of low relief is
150 X, plain light.
heulandite.
58
Clarno Lavas
Clarno lavas in the Clarno Basin may be broadly
separated into two groups:
a lower inter-mudflow series
and a post-mudflow series which occurs near the top of
the formation.
It should be emphasized that the lavas
obey no inflexible rule of occurrence and that mapping
was based upon "lavas with minor amounts of sediments"
and "sediments with minor amounts of lavas."
Moreover,
it was found impossible to reap the two lava series
separately where they were in contact for long distances,
because lithologic variation is greater within each series
than between them.
As all of the observed lavas were andesites or ba
salts, repetitious petrographic definitions will be
avoided, and attention will be drawn totrextural differences and distinctive mineral assemblages.
Inter-mudflow Lavas
Seven miles east of Clarno on Pine Creek, a well-
defined inter-mudflow lava series is exposed. The more
important types are as follows (modes are given in Table
5 under appropriate numerals):
1.
Basalt containing unknown deuteric mineral.
Hand specimens are dark gray and slightly vesicular
with an occasional visible phenocryst.
Light yellow
59
patches of a claylike mineral are abundant in the otherwise unaltered
rock.
Composition is simple, consisting
primarily of mid-labradorite and an unidentified alteration product, probably deuteric in origin.
It occurs as
acicular needles in colloform arrangement within irregular
cavities lined with opaque hematite.
The cavities pene-
trate plagioclase groundmass and phenocrysts.
The unknown
mineral has an index of refraction higher than 1.54, a
maximum birefringence of 0.016, and parallel extinction.
It is a common mineral in Clarno basalts but, owing to
the small size of its crystals, no positive identification
has been made.
accessory.
Zircon, apatite, and magnetite are
Texture is pilotaxitic-porphyritic.
Ground-
mass crystals vary in length from 0.1 to 0.01 mm.
Phenocrysts attain 5 mm. in length and occupy 31 per cent
of the rock.
All of them show marginal resorption. Slight
heulandite replacement occurs in the phenocrysts but is
not visible in the groundmass.
2.
Zoning is indistinct.
Uralite-pyroxene basalt.
Hand specimens are black, dense, and coarsely
porphyritic.
Nineteen per cent of the rock is calcic
labradorite in the form of phenocrysts.
The felty textured
groundmass is slightly more sodic than the phenocrysts.
Clino-pyroxene shows an intermediate stage in uralitization, best developed along twin seams and at the margins
60
of elongate
crystals.
s include
lino
hypersthene and quartz.
ot.v'0i fl:j r'esoi oed
`, he
and surrounded by small cry
-pyro serve and a
thin zone of glass.
aCei:eCl'v is seen
Soy" e
in the largest plagioclase
c
y.
0f the
groundmass pyroxene is alt-e. mod to cc orit,e. lea
c-i i'
the large
calcite are present in association
o
P
Y_
crystals.
Uralitized
basalt.
ecribef but diffe s
t,:
This rock is much like
in its high degree of pyrox.e._e alte:cat on and in its h 1,
percentage of minute, eq.J..y an
netitF
a
disseminated in swirling' pal err
throe }i the g-rounctusas.
on
Broken phenocryStS of mi -la e
cons mitt? t,c
aonec
cent of the rock and are
normal patterns. Over one hundred a.
estimated in one 2 mm. c-'tsta .
has been oxidized to hema tP i g e oY
ivio
O
;COY"itinuL0us
six zones were
t of the :?;a;g'netite
11
p e rs
b...`
a-1 ,
The fresh rock is coal a ggl'ained, black, and very
porphyritic. Large crystals o l"
accurate identification of
aid-la ar adorite phenocr, ,s La
log: the
Lo'
t a _n
n
a
and hype hene.
a
exhibit a high frequency ou
zones. Zoning is often mis
pgro, e ?.e
mn-,
.
and clear, sharp
in alternate ;°dIns or
and
cl
offset at the twin into'
48 per cent.
aC
;'ounds constitutes
lt_
It is compos
c of_LLes o
oA coerce
:ca
labradorite and irregular grains
of:
t tL and
Ci':c:
(11 o
acci ent
in a matrix of anhedral pu_a`'_oc _as
heulandite has occurred wit iin th.
and
nd.. a
o
-
clase phenocrysts.
Andesitic basalt.
This rock is dark-colored with large
on oxide.
groundmass of labradorite and
One
.
a fine, inequ f granu. I ar
phenocrysts of sodic labradoi:
occur in two forms.
l0 ;:rm
is only
margins, passing into vein-',--',',- litr
,a tz drat ins
reso bed on the
in the
(i:e
The other is strongly _esorrbed anc? surrounded by a
mass.
rim of reaction products, ch e '
cc:. untd :nt:if
i-
1 e plagioclase
brown, non-pleochroic cline.. j roxerie.
phenocrysts are also of two types.
euhedral, while others shio s jre.so
e0
fot.:e are clear. a.rid
ta_0
,
t articuilar
sodic zones.
6.
Basaltic andesite.
Normal in composition
tinct i ve lei
-M, U
aye :t;t re,
sections
fragments of this lava were
of mudflow units from several different areas. In place,
it forms thick red flows. event; -ei ht per cent of the
rock is sodic labradorite, an in its rain size and
porphyritic development
J.. v
':;i
l
l! v
e
;a 'UL;dip
j-
r
oG
eile t with i linut
needles and rods of magnetite, nova lar`,elz; altered to
hematite. They are totally:- u_ oor i eint. e and pass through
the boundaries of all other v: our: rass crystals,
The g_'o f? easy 1
already described.
.
Heulandite replacement is cokri _on.
7.
Augite basaltic a
ndes}__te.
Hand specimens are 1-IL pint-colored but the m icroscop:
discloses a groundmass of sod "LC lebradorite and an^-
Large, 4 to 5 mm., grains of
ouu.ar1t_z
are
tly corroded
and are usually surrounded b; small c seals of clinopyroxene. Plagioclase phenocl'ysts 'L,avv-e coon almost
eliminated by resorption.
augite has occurred.
I
;:: ome urali_tization of L1e
eular?.ciite veins are present in the
groundmass.
8.
Hornblende
andesite.
Flow rocks of li ht-co 3_'e C Hornblende andsite are
common.
or
Phenocrysts of m _d-an asa_Le as
mm. in length.
up to 5 mm. ,
They; are surrounded b;
Long blades of horn
make up 9 per cent
of the lava,
the usual corrosion rims
of'
ly 0.'2 to 0.f
---de .
pit. o -d-' zed to hematite.
4
iai in
Traces of uralite in association ith curio-c,yrolxer.e
sometimes contain minute spcieruiites. Tie ,'ronriomass,
-
composed of andesine and hematite,
Quartz and apatite are acceesor;;i.
is ver,, fine-goaine
.
TABLE 5
Percentage 11oluue Uric
:.;de
Inter-1'_z'? av,r T:avas
Constituent
(
)
)
of C1Grno
tji :+) ()
Labradorite
c,
8
Labroandesine
Quartz
"Clino-pyroxene"
Pigeonite
(0)
n
Hypersthene
Uralite
Chlorite
TI
I
J.
Calcite
Magnetite
Hematite
P
2
T
-14
Apatite
Zircon
l;
Heulandite
Unknown deuteric
mineral
T = less than 1
Explanation:
Basalt (T-47)
(2)
Uralite-pyroxene
(3)
Uralitized basalt
(4)
Pigeonite-hyperstnen
(5)
Andesitic basalt (T-
(6)
Basaltic andesite (T
basal;
(T'-'0)
15
T
TAIE)TLI,
Percentage TJo
_. _.
3,
;la=_ r o
Lava o
Inter- `° U.u- '1.o
Constituent
t)
Labroandesine
50
Andesine
Quartz
Augite
"Clino-pyroxene"
Enstatite
Hornblende
of
c _ c==
t9)
(0
78
73
!'
u
i10)
30
3
9
Lamprobolite (?)
10
Uralite
Chlorite
Magnetite
Hematite
Apatite
Zircon
Heulandite
5
2
2
1.0
13
3
0
'
T = less than 11,16
anation:
Augite basaltic andEs
Hornblende andesi to
Augite- and quartzEnstati te-nearing
a
,,alt
(r
I13)
9.
Augite- and quartz-..eari
This rock
occurs as a
tic lava
or"
9
associated with flow breccias aid s Fro zeol_..te min r li-
zation.
It is one of
the most cor; :; o
mudflow conglomimeratea.
of ks
in the upper
Tue nude vine p`leroc°r sts have been
strongly resorbed and are la..-opely _'e` uc-- d to rounded,
quartz are eSent up
1 mm. vestiges. Crystals
eci.
A'
mm. in size and are only
phenocrysts are seldom 1
hay 0.
il..lime ter.
groundmass is composed of
ax-L- ! c,
:U_ u9 irregular
crystals of aridesine, and.".
largely oxidized to neia ti'
10. Enstatite-beaiin
n i u . t .c
,o
Cu r a
_-t:uCryW loV in
1C d
position and probably are
carrels t iv`a s of
.;"
G: re co: )oseci of large
mudflow lavas on Pine C'ee.-.
coded
euhedral phenocry;'Sts of clear
amphibole in a fine, pi ota :.'=t'_(r
microlites and anhedral. Li n o f
is present but newel in a` ; c.-_.a; t_
pyroxene.
rOU-W-IaSs
d-
of stout
.a,_o_ it: ,
5
he
u.L'al '_be
o:L'Gl=fl,
Suggestive of this
magnetite streamers in the
,
t
0-1
It may have devo
now resorbed.
-
ins of L-a 'n£_ tile,
The eastward-dipp_
Creek one mile below Mud
The
ondant
;U.:_;0.
resorbed plagioclase roheooca sta ay
strongly
' tan replaced by
o
mineral was discerned
heulandite, but no trace
The most d__st
the groundma
alc of
is the presence of lay
ably larnprobolite.
feature G ! this lava
c
pro%-
They are
cozona
seen to bri
of magnetite and are pleochna
russet.
Upper Clarno Lavas
Upper Clarno lavas in the C'.:! apno Basi
which occur
deposits.
are those
strati;graphic ll above. all
_ f l ow
writer were
All such lavas examine
Passes of
two
basalts or andesitic basal
ties
leucoandesite. The outstanc i
1. Pyroxene basalt.
as :L o! ! OWs
Upper Clarno lavas in the Cla pno Easin are
pyroxene basalt.
Fine
sa
rj..
cl varieties are characterized
by a trachytic grounds. ass of atoll ei._ -labrad
microlites with small amounts of
,mite,
he
often devitrif ied. In the absence
lites are set in a matrix of anhedi
_rado :Lte,
grained clino-pyroxene and -.:aZnebite
the mei
intergranular accessories.
octahedral, vermicular, and
the
bite occurs
nas
their subophitic to into
.aula:
in
Coarse-
. 1UU_
erained varieties resemble the Columbia
Fine
ba sa _I
: oan a ss of
s in
to
1.0 mm. labradorite laths.
hourglass extinction, is zc: 3r ll a;1
tc..a?
clase.
These
rocks
are the
w.f.,;1
..Vi,o.i'i't,i. . _v1v
lavas that were examined..
J;--
often highly zoned, are
resorbed.
a
Co
Deuteric pr od.ucts are
I,ad.o_ it
.. o
ten
,
;es
a- S L1'ia
iC
0.1.:.._,Gca lc 4-.v', tC'a?4 t
ar
po
d
coi:?ie on.
r-I oC:
::°c,
,1
iron oxides. Modes
in Table 6, numbers .,
2. Andesitic basal .,.
- ewe
w
U.
a t-
IF.
i7e lavas of Sheep
.1..
1C, E.
C
" 1.. _.:a i
of
oe of
c
to black andesitic basalt,
granular-porphyritic,
tat:;. in length, range from
Slight heulandite replac:i
specimens.
ti
'..
-Oligocene tithe, were
v S. ,
,
-/
.h1Ui.._1,,.,
lavas, having beet
1l .
urn o
one
and probably hematite.
1
U....
the
and is always surrounded O
These
Li. .1.
They constitu
Quartz is often
rock.
oJ.
1oc
-
Groundmass
Hornblende and au6ite al-0,
hornblende is weakly zones. and
._... c
(
..
o`t
ado
t
ao
e.
68
altered to hematite.
Much of the augite has been ter-d to chlorite and iron
oxides. Minute crystals of apa tile, i -rcon, and rule
of magnetite which have beer. la
e
occur as inclusions in felds,oa
u
`. mode is given in Table
6, number 5.
3.
Leucoandesite.
fry Creek leuco-
Extending southwestward from the
andesite intrusive (p. 50) are thrice flew rocks which are
similar to it in appearance and composition. Finer grain,
lack of heulandite replacement, and finely disseiinated
magnetite are the main differences.
The n;;a gneti to is
partly oxidized to hematite and limonite,
rock is given in Table 6, number
Two large outcrops
sections 26 and
of altered
27, T. 7 S., R. 10
rode of
t:,
s
leucoandesito occur in
,
on the.
stions o:_ intrusive origin
Several
are present, but they seem i nconclu.si
rock is
petrographically similar to the le;.coandes_tes of Dry
Hancock Canyon.
Creek but differs in
its
content of iron oxide and
hornblende. In some parts of the
the phenocrfists
are replaced by chalcedony, calcite, or magnetite.
Secondary alteration of the latter produces hematite and
limonite pseudomorphs. Much of the plagioclase was reduced
to a white clay during late Aocene v- eat Bering. A mode of
this rock is given in Table 6, nu be-o 7.
h .tb err
Percentage 'rV1ai..e I C
Cla .:iD Lo'c
1 DT
..
Constituent
(1)
Lab ra do x' I be
Andesine
Quartz
Hornblende
Uralite
Augite
Hypersth.ene
"Clino Pyroxene"
0
GlassMagneLie
Hematite
Limonite
Amatite
0
v
T
m
Huts le
Zircon
Chlorite
I
`'Clay,
Calcite
Heulandite
T = less than 1
Explanation:
1Jlly
( a ) Fine-grained upper C±
T. 7 S.S , H. 20 E. (T`7
2
J
0
.,,
o
-
0.4
Same, sec. 29, T.
Same, Sec.
Upper Clarno coal°e
Sec. 32, T. 7 S.,
1
; '. il
.
(J) Upper Clarno andesit-c
Sec. 19, T. 8 S., R.
'v,
2.,
2.
(6) Dry Creek leucoandes
(7) Leucoandesite, Secs. 20 a
(T-151)
.
b-
(
(
,
'-L
!
1
;ca
1-7
'- 8
.
Spherulitic basalt.
This unusual rock is found in the
cliffs on the hills southwest of Fossil.
show platy fracture with
east;-.'acing
Hand specimen
ion occurrinq between
the
small, 1 cm, or less, apt e._ :z_
decomposed samples may be
'tee,
u! c
ar,
the
ha. tt, ned
leasing hundreds of little elt :te and
of matrix.
ments
;u
Under the microscope, tiny bla
in pilotaxitic arrangement
a bead on to
,o_a encicd in a
__
its up to 3 mm. long, auJi .'., end pe
Magnetite occurs as a fine
distinct grains between c
chlorite and clay.
Patterns of oval and ellipsoidal
by zones of chlorite and iron o-
t
.
uninterruptedly through 'gin
they are similar to some
this rock is given in Tab:
oondma
l
of pyroxene granules and
tected under crossed nicol
C7
tic
:ne
are
..
°< dor
nt.
p
no
t ti on products Ere
.vie are outlined
can: of
be
Politea pass
ae tL
o!
re-
in
t
cidiana.
a, number d.
e c lJ
mode of
C r y S J I'111 Ga `U, lOii
A fragmentary record of the development o ' Clarno
magma is to be found in t'ha. pla ioclase p`:ienocrysts.
1
single thin section may off _ ee ;,int,lu ine<aha us table
not entirelvariations in crystal architecture. This
due to variety in crystal makei,_p.
e
anal om orientations
of the cut section, relative to the phenocrysts, add to the diversity. The follow"n- observations
and positions
were made upon
phenocrysts cut normal to ("".10) and ,,hl_ch
it degrees of tree
maximum plagioclase extinction ang= e for the slide.
The largest, and pre suiab14/ the oldest, plagioclase
displayed extinction angles Uv t17
phenocrysts usually contain an unzoned core,.
This may
indicate that equilibrium p_revo-ilea cetv.ee? the magma and
embryonic crystals
or that tie section is parallel to a
single, internal zone laye-er.
Most of the volume of the olagio c ,ase ph enoc_r'ySts is
discontinuous
taken up by a complex system of
normal zones which probal' , ,T reflect e:cap tive
the surface.
activity at
Several observations s ,; ;es c that p 'essure
was the controlling factor in the development of this
zoning.
Plagioclase
zoning--
is usually interpreted as a
to fluctuations in ma ma temperature, fi?e melting point of minerals like feldspar, even in pol`, -corrlponent
response
72
increased pressure (1=',
Investigations by Tuttle and Bo len (3, p. 497)
silicate systems, is raised
p. 64).
show that this effict is greatly enhanced by the presence
of volatiles, especially in the range 0-2500 kg. i cr,;. 2,
corresponding to depths oz' 0the system to a pressure
files.
The response of
release would he the same as if
temperature were to drop sharply.
temperature supersaturates
A rapid decrease in
the liquid in calcic plagio-
clase, causing accelerated crystalli_za'ion until equilibrium is attained or until the plagioclase is entirely
frozen.
Zoning in Clarno
breaks which terminate
latias is characterized by sharp
individual continuous normal zones.
A pressure release at the s dace (di1J_c'ti there ,must
no eruption would
occur) should be experienced by the
entire liquid reservoir almost ins tantarieou ly. In contrast, heat transfer in magmas is thought to be very slow
(42, p. 209).
A series of eruptions may cause phenocrysts of the
magma chamber to become heavily zoned. only to be destroye
rl
by intervals of increasing pressure and temperature. The
fact that large crystals with many successive ' unconforrni-
to gradual cooling of the
entire system or, more likely,', the ascent of the crystal
through a pressure gradient toward eruption.
ties" survived,
may be due
Minute, euhedral Inclcal_on.e of app Cite, z rco, n, and
1.
rutile, in that order of abu:n.danc'e, are found even in the
hti 4r al rays total less than one
cores of the phenocrysts.
per cent. There is no evidence that they acted as "seeds"
to later crystals. Another' commonly included mine al,
particularly in andesitic bacalts, is chlorite. It often
occurs in thin, concentric bands :hich closely follow the
zonation. It has probably resulted fm or tie early breakdown of some pyribole.
Hornblende, clino-pyroxene, and quartz were fork pled
together with the plagioclase .,henocryste. Their order
of crystallization was not a-eter pined in tt e laboratory,
it probably varied.
A further stage in f lar ; ar ie reeoo e.L is recorcer
ice of o t
in the relatively thick continuous i
0_.'i".7a
a'r p_'esa?7.r eproIJa c' uv
zoned phenocrysts. They
r, e y thin,
p a began to fall during the e-_--( --U, z
have been
an(J,
zone often succeeds this
c1ea
'
during groundmass
crystallize lion,
is
fgroundeass composition.
The final stage off' fold
r
_
de- elopm;er)t
1,
s the
freezing of the groundmass. frail ar:;oun'-s of pyrorerie
o_ rrd<<,a s are
he
% ,;._
e
were often included. Co
the reaction products, c lorite sud ma,cnet:i_t from a
_
late breakdown of the
ho
u_de.
ti,
;
C
}`'
.
L
eric
adjustments include clay minerals frolic pla.cl-J oclase and
uralite and chlorite from c 01
to hematite is partly a proc u.ct 0
partly a deuteric effect.
o r' magnetite
O1 i Aa io
s
.
face G c ache 'ink;, and
Strong evidence suppo} rs the co zte: ion of Emmons (1.0 )
that polysynthetic twinning cf plagioclase is a late t vent.
When a crystal, whose zonation is clearly stow, by contin
ous bands of inclusions, discla y s zoned e:r Ui ction pat,
only in alternate or ser i-alteL
that twinning followed zoning,
t
u
;
6 Luis deal,
,
In some i is`c aL ces the
aced along
zones, while not eliminated., are s' arol<i d i S
twin seams. As a feature of cr al
di i la
ve
would deflect the zones bu
-' i
lative suggestion is that ti,t;ch .ati`c
.'a
take place during an adjustment
to low tempe =a-
Ly
o
r '_ ,;t
g:
A
specu-
f1- ement i::.ght
ture forms of plagioclase.
The 'Large accumulation of J-not la `>tl
welded tuff units, and the afJ bill:
alteration clearly show that C;la : no
at vial, the
'odt;cts o
a'' i:; w 5
charged with volatiles.
Secondary alteration of the laves and
er
lieu enic
highly
usl %es iS
first a process of oxidation., a ec _.it the iron- ich
minerals, and second a process of r Ydma cfo , converting
the entire mass to clay.
75
Some additional fem.'s. eS of l:. iii::
C
s) t
a
" ti , cu..
C)
n
deserve attention:
1.
Late emplacement o
eolltce,
As a product of late cs
or lava, excess silica
SOlved
in not
UTa lJC^r, may
Cc v.LO
Z.
i.
vi1.LLi
firs, di.S-
ade _.y c,=.l:
v'(1t'
a ta czi aYOi
L.
trio :agu5
i7C)l e ca-i -_ h`.',
vO
f or'mi heulandite:
CaAl 2Si2O8
pins 2k
H1CaA12(S'03)6
The above reaction, with
i0
l :r 5 H 0
canal s
°
pp-rOp
ate cod... Rio ations, iS
tons suitable for
probable source of solutio ns lob
making heulandite, stilx it'e,, and lauconiGe. .. auenched"
example may be seen in so ; er a ea quartz tihenocrysts,
..
particularly in dikes or other situations where slow cooling in the presence of dies e inatec. steam or 'not water be
u tE; is Sc2iia in ouch constant and
possible (p. p7). Heuland'i
exclusive relationship to the resorted Quartz that em-
It should
be noted that the heulandite structure is unstable above
placement from an external source iS ruled out.
(15, p. 645) and that. 0-1-1. instances o: Its
occurred below
st
fag
crystallization near the
177° F.
this temperature.
relations are
If tine above in
correct, the embayr'ient any. round
can take place in the final at
q-,
of
oo L air'.
`.1S U
Heulandite, in the above reaction, occupy i.e;_ nearly
three times greater volume than the a niort'1:vte it replaces.
This may explain the
:i_
zeolite replacement of caIeJ_,, zoias and cones seems to
.:nest n _;
ri Uspill out" of the phenocrya ins `x: o
veinlets to permeate the
Heulandite replacement
F1
,as
.
not found to bc:
c-rite °.ion
a
of intrusive relationship. Faults one e;oint ne o Sienna
and
intrusives often contain
o
fz e o l vto z:- a ti a s re
laur,onite. Amygdaloidal -1"21-111
.'Li ,
J _4 .
a
.J
G
.+.
Glares sediments.
Zeolite veins are abundant
chin sectof the lavas and sediments examined in thin
ioclase phen.ocontained heulandite replacements of r
com mon.
trysts and groundmass.
2.
Resorption of quartz in
salt e.
The common occurrence or quartz In Clarno i )a salts
that do not show inclusions of other roebs atron , i v
;n: st bee cons
prima
suggests that the mineral
stituent of the magma at so° e >ta e in its development.
Significant in this respect is sue lack of cr_1_vine in any
of the Clarno rocks
examm.m1.nee_.
Greater complexity ,,,as noted _ n tl
a
J. 'ii anon O
quartz in basalts than in ann.des tes, Because of its
O1 en
and. soda
higher content of iron and magnesium,
feldspar are formed. The formation of complex hydrous
Fig. 10
Photomicrograph of plagioclase phenocryst
Core (white area) is
in Clarno lava.
largely replaced by heulandite. Note
heulandite streamers extending into
50 X, crossed nicols.
groundmass.
pezeolites, as occurred in the and.ecites, is ai ; .ce"nti
crop
vented by the higher te.: evo t?_:
t
Four molecules of silica nil! die pl.a u = e l in m from one
the pls ,_,iocia
molecule of anorthite
e structure if
to eplac_ the calcium.
univalent cations are a are.
probably involved, The result
Soda, rather than pots oh,
is two molecules of Mite and one of lime:
CaA12Si208
2 NaAlSi3O8
plus
eu
t
_0
C10-
Plus
As the CaO is highly reactive,
surrounding minerals not already satuw
with it. These
the extent that
_
=CA
are primarily quartz and magnetite, To
2'ous iron in
t
magnesium replaces some
(248,
p. 85) and joins
pyroxene in the diop
CaO
ca,
it
ode
M aso
...
plus 2 Si02
equals
0,
Ca(Ng,Fe) (Si03)1
0J3.
All of the above
o__'odi
is were seen
, with the
thin section in the expected cla ion._.
itered into the
_,t
ception of hematite, which_.
zone
production of chlorite
of clear glass is soy.,
pla ioclase.
nI
conic
79
The recorded portion c
in time. The fact that1 the
the secondary feldspar, wern
_
1
process is POE
`
..
tJ s',. .-1'
L.GLi_t_lii
C::(1 I
a
_ e.
reaction and in the pl of _:: spGtiel
..__
of
C.
iona`
strong!-,.,,-
ation of the
suggests that they were Zarand after so
entire mass, The roundod
products indicates that
_0-
pea c
no
to
..Jig
were
of
carried away by the sorvou
Magnetite, hematite, and c a3 _cedon5 esondo't onpas
3.
hti after a
Iron oxide oset do
pseudomorphs after felt
plugs.
As criteria of
o
winarals should be
the
,
used with caution because the, are
v
3 intrusive
_f
seen
i"1
ha redo .y.
, rh i bo F and
r
sensitive to
surface and groundwater conditions.
Sequence or N.
Calkins (6, p. 170), i
concluded that Clarno lcv;v
cific evidence
::[1o"';,
follow
elt
order:
4.
3.
2,
1.
Rhyo l i t e
Quartz Boca_`
Pyroxene Andes_
Hornblende Andesite
-,
The present writer is i
analysis.
a
in the Cl "no
The lower lava
well as mudflow units
:c with C a
a _ _,.
e low is
_.
:>i
i,: s t
as
d'ominaii.t!.'/
at
andesite with a lesser ;Tolu.._ of
The intermediate
forms, basaltic andesi:,c and
r.
The upper lava series in
Basin
.,
__
Uasalt, also occur.
Esal ic witk the ex, andebite
ception of two large leucoLndesiO
__
lgnimbrite, and other d
be rhyolitic. More detailcd
identify eruptive trends within r_
s which
-e..
The frequency with which quepQ
ould
ec
_
maO,;
:7 to
ena2a
330
1 _,aa ti
an odd comb i
containing calcic fetes
t; of plagioclase,
Lion of stable and unstable _ :.or
rrras a
strongly suggests that a trio of lift..
often occurred prior to yr _.; _ .i_oi.
each
follow
inter-connecting chambers of Cla _ o
i
its own course of di ve loo ent but in
_..tt
ztl, affect
expect a
Tould
the history of others. r i
definite trend in differentiation to b eco de
surface.
Clarno Volcanic iron to
c tea a't-i
eCCIa
General Features
ant
One of the most Cony t
logic types of the Cla:rea
[la='< c uorio ;
tno-
_
ii;a tion
ne0US
mixture of coarse and.
mudfl ow origin.
They
a' t,
510
0
or low hills, but local
(11 0 Of"
cliffs as in the "Pal, isa '.e `,o
11) .
-IL
1,11
-L
White and yellow
green, and brown
Ci. --r-
also 0005:
are seen to cap
)(7
of lava
;ti
disintegration and re o a__
may result in pock-mac
".)...
r;ce
Thick accumnulat_o-rn
tributed in central 0
:or
they occur near Fossil,
burnt Ranch, west of _:_
Post, on Rowe CreeP
C.?
_
_;ee:_
(i.d
"r
a_cto ;
;ioL'.l
-
-1
_
11 -51
o
c;,
arc
in the Horse Heaven
with lava flows, they
formation. Until
methods of identify 1.1
should not be retarded
e se
110
Fig. 11
The "Palisades" on Pine Creek.
Clarno mudflow conglomerate.
Lithol ogy
thin, : ine
A typical sec
rained, well-so.,
silt beds separatic;
.;b
grain size from c_
:a
p
sand and
s
A0 0 which 2a
'la
_E
tons,
horizontal ac
extreme over short
from 1 to 20 feet.
intervening tuff
ms=
feet.
eCL
Individual .re.
feet to about a
of rounding, and co
most favorable ciren
sent.
may be toe c _ a
r
N
n e an
.1
a in size, c
.
'_
20 H. , a Clarno ? ;.,
outcrop or
c
e
The
e
only under the
in section 2
ancee,
...,_ _ .r.
N,
poorly
strstif
breccia are so related in attitudes sna comp
suggest an incise volcano
gradually westward u,.o_ oa
.'
t
er of
R.
f 1ovw
_
zc
_
b S. ,
.
as to
i.
o n.
pa
a ser
>ll t eddeCd nudflow
conglomerates in
r..
ohether
. forma
Mono
or fine, is that c, the s .1..,
containing lava,
a few localities however, ,..,.
chert, quartzite, 00 ' _,_ta3 and <;ranitic rococ are found
The
outflow
composition
_
_
in the volcanic sediments, This e.t., .._
near the center of section 24,
a
-e-f.
do seen
may
_1.
southwest of t
co00C'!es-i
aec ion_
50), and below
27, T. 7 S., R.
t
forms part of the
Thin section.,
older Pocks
'v iI : a t
Clafno scU
> _o _ from
ho.:
occasional rounded Ina tul
solidly packed
4..
n little
interstitial matrix,
compact as to re»e...,., l:
nents
-ca o._
l..
stain is so
..I. iJ! c a i.LC.e-
o
site. Lithif ica t.-on has
s o l v e d . come J:ecr°'ys-
tallization of the natrix,
specimens, no cement tai
}.,
and on]
in some specimens.
a
to a rock
ava
Low even
was
.'a.
m
'Cies
cas
Lion contains atundaa;
u
MR=
en.
o3
{' -_ a c -
man-.,,r
Occasions
hE. L1 :. c' ndite.
which are partly replaced
ins in the matrix.
zealites appear as replacements a
ers from lower Fine Creak:
Quartz is not common.
contain abundant
that strongly I"eti>i..i..L C. welded d
-colored
Upon weathering, t'_:_face0,,a
altered to clay
of chlorite is a
outcrop.
<<4!f>7.
One tyro
lava, not
7ily distributed rod-oha spec[
seen elsewhere, contains s
magnetite in a la
too and other glassy rocks
r_;lpents of
Ioo
a , La.'
co..nC7os
a _r!o and lava fraEments are
is and chlorite.
One common
and may
variet,,,,
color the entire
Structure
conglomerates and.
In general plan, the uuid fl
breccias of the Clarno Basin are separated by a series
of lavas into an upper sec .,once about 0C feet thick,
with best exposures near Mono, and a lower
ence
c1
more than 1000
feet thick. with
beat exposures
Hollow (east of the
The atti tude3. of the two sequences can only be com-
pared in one small area on lower Pine Creek, about
miles east of Clerno 9
appear to be concor ant,
`'lhe'.
In the eastern half of the area, the mud, low units dip
t
about 6 degrees NW, and
westward, they become
Traced
structural terrace.
road
om
3
of the terrace
tern mai
passes through ;la no in a Pb 60 E, direction and i
marked by an abru
west.
Eastward-
0
outcrops of
downstream from Clarrlo sure
reel to the nort
a ,(Ju't v 20
i
Mow ; o n^
Oir a tP
;t the presence of a 5uriee
syncline west of Cla :°no (see Fig. 23).
ar trend and small
Innumerable MOO of
placement are evident
Slumping occurs where the
WW..
f
content
12).
p.
'I
A
•
Fig. 12
.c
S
Clarno inudflow units in Palisades.
Note (A) lensing and (B) small
displacement.
87
Origin
Sediments having the characters just outlined are
known by the Javanese term "lahar" and have been observed
in process of formation in volcanic regions the world over.
They are universally of mudflow origin involving waterladen volcanic ash.
The source of water varies. Erosional
breaching or eruption through a crater lake, contact of
hot lava with glacial ice, direct condensation of volcanic
emanations, and heavy rainfall have been cited.
Mud
eruptions resulting from water collected in active craters,
as in Java (37), could hardly account for the great volume
of Clarno mudflows.
Climatic limitations rule out glacial
Anderson (1), in a discussion of the Tuscan
formation of California (which is almost identical to the
development.
Clarno sediments), has compiled many historical references
to mudflows known to have occurred because of rainfall on
volcanic ash.
To overcome, on a large scale, the binding
effect of a dense plant cover, Clarno mudflows must have
originated on steep volcanic slopes, mantled with loose
ejecta and subject to frequent heavy rains.
The prevailing environment of deposition was one of
quiet fluvial and lacustrine accumulation in which sorting
was possible.
The dominant sediments, in terms of volume,
rere deposited during brief interruptions of these conditions.
Rivers of mud, choked with lava fragments, poured
88
intermittently down the drainage systems of nearby hills
and spread over the broad surface of the Clarno Basin.
That many of the mudflows came from the east is shown
by the rocks contained in the deposits and by the direction
in which fossil plants, firml rooted at the interface
between units, were pushed over by the succeeding mudflow.
In some places, whole forests were undoubtedly overcome.
Fragments of poorly-preserved fossil wood parallel to
bedding alignment are common.
Upright trunks are
occasionally discovered.
Clarno Tuffs
General Relations
Tuff is probably the most abundant Clarno rock, but
it is usually mixed with. coarse material in mudflows or
breccias
only thick or continuous deposits of fine vol-
canic sediments were mapped as tuffs.
They are predomin-
antly brick-red or less commonly buff, green, or white.
High in expansive clay minerals, they swell greatly in
contact with water.
Winter rains and the long summer dry
spells cause the tuffs alternately to expand and contract,
producing a characteristic '`'popcorn" surface.
Several authors, especially Waters (43), have called
attention to the "ancient soil at the unconformity above
the Clarno formation."
The present writer believes that
89
Waters' ancient soil in the Horse Heaven district and the
red tuffs at Clarno are parts of the same unit, related
in time and stratigraphic position.
There is ample reason
to doubt, however, that either one represents the top of
the Clarno formation.
To quote Waters (43, p. 126):
"No reliable date has
been obtained regarding the age of the clays at the unconformity and of the post-Clarno rocks above it."
But
they are, he says, "of considerable importance in solving
the stratigraphic problems of ' central Oregon."
The Horse Heaven soil layer is underlain by a series
of andesitic lavas and mudflow deposits.
true of the red tuffs at Clarno.
The same is
Unconformity is common
here as throughout the formation, but it is erosional,
not structural.
Above the red soil at Horse Heaven is a
complex of rhyolitic rocks, called "post-Clarno" by
Waters.
They include a distinctive welded tuff, much
like the Clarno lower welded tuff (page 101), which occurs
just above the red soil at Clarno.
This welded tuff
thickens toward the Horse Heaven area.
At Clarno, a thick series of andesites, basalts,
tuffs, ignimbrite, and two welded tuff units separates the
red tuff from the true structural unconformity which marks
the top of the formation.
The "post-Clarno" (post-red
90
soil) rocks at Horse Heaven are probably also Clarno in
age.
Lithology
Thin sections of the tuff were prepared. Sixty-five
per cent of the rock is a fine clay matrix impregnated
with hematite.
No trace of a vitroclastic texture remains.
Coarse particles seldom exceed 1 mm. in size and are com-
posed of pumice, acid lavas, andesites, basalts, and.
coarse-`;rained tuffaceous sediments.
Crystals of plagio-
clase and quartz are common.
Grains of ma netite are
present but have sharp, unaltered margins which contrast
with the abundant matrix hematite.
Clarno tuffs tend to become red toward the top, and
some John Day tuffs are red at the bottom.
Where no lavas
intervene, the two red units may lie in confusing contact.
Slumping usually complicates the problem.
In the writer's
experience, color distinction is of no value.
If samples
of the same size and shape are placed at the same time in
containers of still water, that of the John Day will slake
and atiell many times faster and will remain suspended much
longer after agitation. The red John Dar tuff contains
many small pisolites which seem to be lacking in the Clarno
tuffs.
91
A,12 'e
In the SW
1
SE! of section 27, T. 7 S., R. 19 E.,
bluffs of light-colored, well-bedded, tuffaceous siltstone, sandstone, and conglomerate stand out, because of
superior hardness from enclosing Clarno tuffs (see Fig.
13).
Known as the "nut-beds", they have yielded a great
variety of paleobotanical material.
More than 25 species
of fossil woods, some containing faithful representations
of fungi, have been identified (34, p. 58,o,). A wide range
of angiosperm seeds and fruits, many of them perfectly
preserved by opal and chalcedony, have been described by
Scott (35, 36), who compares them to living floras of warm
temperate and subtropical res" ions and to the fossil flora
of the Ypresian (Upper Lower Eocene) London Clay.
A rhinoceros tooth of Middle Eocene affinities was
discovered in the Clarno red beds just above the fossil
nut horizon (39).
Near the east quarter-corner of section 27, T. 7 S.,
R.
19 E., an important fossil locality in Clarno tuffs was
brought to light in
1953
by Mr. A. W. Hancock, a well-known
amateur paleontologist of Portland, Oregon.
Under his
supervision, several tons of plaster casts, containing the
fragile bones of many extinct mammals, were recovered.
The results of laboratory studies have not appeared in
print, but the following tentative identifications have
Fig. 13
"Nut beds" of sec. 27, T. 7 S.,
R. 19 E.
Note overburden of
dark Clarno tuff at top of picture.
93
been made at the excavation site (19):
Titanothere (very large)
Hyracodont (running rhinoceros)
Oreodont (probably a Merycoidodont)
A pre-Mesohippus equid
Tapiroids (several sizes)
Creodont (probably a Mesonychid)
Amynodont (water-loving rhinoceros)
Crocodilian
Small fish
This list is necessarily very conservative; many more
forms occur.
Although much work remains to be done on
this material before an accurate age can be assigned, it
is within the range of Upper Eocene-Lower Oligocene.
The
large size of the titanotheres suggests the latter.
At present, the fossil mammal locality at Clarno is
the sole opportunity for precise dating within the Clarno
formation.
Unfortunately, the position of the deposits
with respect to surrounding rocks is uncertain.
If they
are a part of the red beds on which they rest, a thick
series of Clarno lavas lies stratigraphically above them.
On this basis, the Clarno formation may range well into
the Oligocene.
A basal gravel, consisting of chert and
other foreign rocks, coupled with the lithologic dissimilarity between the tuffs and lower units, suggests that
the mammal-bearing beds are not correlatives of the red
tuffs or nut beds.
If they are a later deposit, as this
writer believes, they were formed on a broad plain which
erosion had produced on lavas and tuffs alike, just
94
preceding the catastrophic eruption of Clarno ignimbrite.
On this basis, the uppermost Clarno is Lower Oligocene in
age.
Structure
The attitude of the Clarno red beds is that of a broad
rolling
surface,
descending gently from the east toward
Clarno, then dipping sharply to the northwest at about 20
degrees.
Crude bedding is evidenced by vertical changes
in color.
The usual color
is buff, green,
sequence,
from the bottom up,
red, and an occasional streamer of white
at the top.
Thickness
A maximum thickness of 200 feet was measured at
Clarno.
ties.
Slumping exaggerates this figure in some localiThickness decreases eastward.
Environment of Deposition
1.
The Red Tuffs.
The Clarno red tuff is actually a clay soil weathered
from tuffaceous sand and volcanic dust.
The coarser
grains, representing many types of volcanic rocks, are
still fresh, but the fines were probably altered as they
accumulated.
Their existence is not due to long-continued
tropical weathering of bedroclk, but to circumstances of
95
Therefore, red tuffs should not
pyroclastic deposition.
be looked upon as time horizons valid throughout the Clarno
formation.
2.
The "Nut Beds".
A glance at the geologic map (see appendix) will show
that extensive lavas were poured over the tuff in the NW
of T. 8 S., R. 19 E., during its deposition.
In the
vicinity of the "nut beds" a distinctive, highly weathered,
amygdaloidal basalt flow occurs at about the same horizon.
Vol-
A lava dam may have formed across a stream channel.
canic sediments then filled the resulting lake in a few
seasons, as evidenced by the abundant fossil stems of
upright Equisetum which transgress several layers.
A sub-
tropical flora grew nearby, adding leaves, fruit, and
stems to the deposit.
Scott (35) lists ten species of
dicotyledonous fruits and seeds representing eight genera
in seven families. The fossil walnut Juglans clarnensis
predominates in two adjacent layers and probably was
washed in large quantities into the lake during storms.
Second in abundance is the boat-shaped nut of the family
i4enispermaceae.
Other fossils probably constitute less
than 5 per cent of the flora.
been found.
The remains of fish have
According to Scott, a majority of the Clarno
species were climbing vines of a humid tropical or subtropical, riparian habitat.
The aqueous environment
96
probably dissolved silica from glass in the tuffs to
provide chalcedony and opal which cemented the sediment
and replaced its fossils.
3.
The Mamma l-Bearing Tuffs.
Because much time is required for the proper extraction of delicate fossils, only a small fraction of this
material at the Clarno mammal locality has been uncovered
(see Fig. 14).
For this reason, only a cursory treatment
of its origin can be given.
The lower part of the deposit
is composed of highly weathered river gravels containing
rocks foreign to the region, set in a matrix of tuff.
Above this a light-yellow tuff, lacking good bedding, is
perhaps 50 feet thick.
i.gnimbrite.
Capping the deposit is the Clarno
Fossils occur as v,rater-worn bones in the
gravels and as scattered remains in the tuffs.
Much of
their fragility and distortion is due to slumping which
has occurred along myriads of small displacement fractures.
This slumping may explain the discontinuous occurrence of
the fossils, as well as the minute fragments of opalized
bone seen in all thin sections of this material.
Under the microscope, the tuff is texturally similar
to the more common red tuffs.
About half of the dust-like
fraction is unaltered, and the remainder has been weathered
to a limonitic clay.
Fragments immersed in water require
hours to slake and swell as compared to seconds required
/- `o! it j+ !
.4
Fig. 14
Excavation of "the mammal beds"
Sec. 27, T. 7 S.,
as of 1959.
Note
resistant overR. 19 E.
burden of Clarno ignimbrite.
111
by the red
tuffs.
s.
It seems strang
in this
,U,!__ animals should be
so
small area.
a
the
,:
averitable
No one. can guess how man-,\.-
graveyard of jumbled
additional fossils have
e
_.
C.st,o,
or what
4;i
may yet be concealed
Inc that a stream,
One may L
bound, would
cal
its
on the Eo-Ol_'<wa
_'0b.,_b.:_y
westward-
unJleis a eve]
Clarna Ra5in flood plain.
.i..
forms
supported many
diles, and fit.
lop
diminutive foum--
d
The
Jco-
cl uo
to no0.1 3x05 coe f e..:
r
wit!
o eohout,_
rhinoceroses
browsed upon the lush
All of
creodonts were emoted
animals and ma
n iJo
river gravels and
The
c_, e._t._n
environment which attract-
informative ecoio_, , of
research.
provided an
s
11
es of animals
keep ahead
and it provided
preservation of fossil
tuffs.
J..t%C.:.L
influence
of the lateritic soil
v nom,
_;e
ea'_
prevented
detailed and
ec,onan uc.1.40;:-1 must await _,._ tun
99
Definition and
Under carts ._n
with volatiles
ebullient liquid,
in a
astrophic in
conditions
can
1
o. ro 4
Naterial are cat-
such
Ds
,onsc:nt,1
augmented in volut
in heat
AU
cx
,o.
suspended
0 10M
S
in power,
can
by the
intensified
and
..
..
ODD-,
hot lava
gas from an u__
vents carried forward
solidified orodoc_ _ ,
):JU 55
comprise a
:-
cOl:Li;__....__
1,.
hf
.._
The
havaS a:ni
pyroclastic tuffs.
Five such _."_ n yovi
They differ free o;
not
of classi ica
Deposits of
-
by slight ear
intense as to
of the
original
o
anion
These are usual]
product of very
huC
,,e,
oc.i_aa U_.
due directly to
joined
isva6 or tuffs.
)
on
en-
tu1
are
e .r' particles
ion_0,
a__
s
Md
... v
corgi
o00
census .
i
the
?eat wa
only
may we
be so
e: ra =
ignimbrite is rest
biL i which have,
the most part,
(l
fo,-;
ilner of no ;iai lava
flows, yet contain an intimate i_. e of i9 c o I _'.6 3sed"
0ti of effervescence in the
pumice fragments or oal
io e of the roundcent
"glowing cloud."
..,
mass of
this rock must be
ini
Welded tuffs and
=_ i e
{
_f _.
contain fraEments
_
t e,
We
llieu 2301
of z oreiwn rocks =_nco:; ,;orated. into the
bottom portion
The region
__
lair .ed
4x2d,;
poonly welded,
t
the
the most dens
"
The
U
;io_..
e
to
apes of heat
wn" c! ut and ±O i ei :> l,. q,iass
It con
shards and fragments of punics. The upper SUM
preventing Me rap
:Fst
porous. It acts as e
occur in the interior
flow
loss of heat.
ar
causing teardf o p clan a !,ioi: in the vesicles, Columnar
jointing is sometimes
As stratigraphic units. welded tuffs frequent!; have
and
load.
J sJ
.;
wide extent and conspicuously uniform c thickness.
recognition and ca- ..
within confuse
'
.
u udL
PI(
volcanic provinces,
map of the Clarno Basin was drawn wi
units.
Their
correlation
"ceo of the feol
aid of these
Clarno Lower
Two welded
t..=6
within the Cla no
any one i;n
.. oe i...
t : were discovered
This is the first reportea
'.,ion,
the pre-John
occurrence of nuc
Mv
formations of central Oregon.
The lowermost. here desi
o lower
eca
welded tuff," is near the to;_ of the f arno section.
occurs in two small outcrops
river in the north es ,
Within the mapped area,
on opposing ides of
corner o.. section --9
and
zo
n!0_.
;
of s
The lower G%. f. t,at'. i
,.pE:' co4iC;i:'ea,
tion
T. 8
at both localities. Large
but basalt overlies the
outcrops of the sane unit ap> ea.. on .she buddy RanchAntelope road, a en miles west of Iu:dc y Ranch, it is
sen
the ,rgorse
probably a con: el tiv of ivila r pock
_
1
district to the southwest.
Hand specimens
fragments of
ndl porous chalk and contain
l Oa
Clarno, these :i'_
U
.
.l. on.:
Ranch, the fraEwants are
or more in diameter.
of
any.
pock.
West
Mum
ape commonly
0 U,
p°
a. :.1(11'1
ounce.
dull white,
; specimens contain
fresh
featureless
rust-colored,
,ci
G,.
make up less than
near
ce
wax.;
association with
o ab,
mo 'tmo' _l l oni te,
-
Thin sectior
mOL'1l10i1te altered
o .J ._. c
_.
texture
the fine wound-
It is
ithout fracture
rioi
e_ t.
mice
Fragment".
is usually
crystallized into
tepe'''_ to nonS
pumice
on
:1 _i_ t
nel as the
Broken phenocryst s
..
i`
,->
Co size
ant 0uou
produced the oe i o.;e
_
.-
ou
tite i'.t.d
CO11C of
obsooved,
Two modes are given
Tab
I __c
0;:o
L2).
Inimbot
e a at cla2no
Nerriai: <
made of a uniq
from the Ferry
Cal Ir
the "andesite or
_"
are
described
cots as plant fossils
the "ash bed" (the
(25) drew
' e J.
mistakenly
identified coil
Mackay
r Or ;ia
to the magma that
zircon are plentifo
Clarno
hock'?
oOndm0ss.
an eo__rle,
Soneu
KOT
he
a r' '.
roer. of or hero Itos,
of it is def or".;ec_
are very clear
pattern. They w r'..
_,icles of de vita
,.r].-out
glass which ar
s ions .
want-
U3
mm, in size.
mass.
of
1._
teo."
Outcrops of
townships,
it
distance west
for an unknown
L _ fa
,01 i:
-:
of f ayno.
!on; O u
removed by Ol
br
L11 it e ,
c. in fo z_
c0vL:_
thick,
50 v to 6G _ _. eLi
hills and rid
e
ing surface t,,7o_,.o .,
one found
,;_C L
degrees to the
The is nimbl
._
dipc
o,
ap11o_.J_::;a
he rock at
.
crops is usually 20 to
slope gullies or on t.,
Fig.
Original
feet
:,
su ,._..,s of
LDP
.JLL
_,. i
...
i
found i
omt1c_ ina_
.. 'F:
Lo n
:3 .
torci out--
,ao
thick &nd
e
upper wielded tuff
I x,y e
they merge into
......
_
.:l e» e- ,1
:J _ L 1
._.
poo
i..,_
or Pie _3
,1,tG.
em pose
o vulcanism in
the Clarno basin
it touncates Clerno
lavas, riudflooss,
VA. undulating i 7 r s e
of late-stage
with an- u1L.L° uncon-
or
a
fortuity by the o
Dikes of
source of the iEnlwbrite
t
Ved to
alicuubThe greatest l.h t'lJlC1; _ variation iB
F_
the top, the
of pre-John Day
'J .' f
C iccil.
l
c.
_cE
_,eai">
white
poorly
ash containing s_
quartz, and to
plagioclase. h'
r, e
of
e;;a-
CIA
e_
_ m _ _._o
-,
,
,
because
Fig. 15
Outcrop of Clarno ignimbrite
at Clarno Pass.
The main body of the cc
weathering to dark yellow or
crude. The rock is very
as glass does. All parts o
pieces of compressed
vcJ
d
pumice,,
Their drawn-out tube s true
gradual change was noted in ILK
pumice
e"
fragments from round:
,o
art -
c)
e
an
__
_ t? e -i ti
t rv
ai
o-''
horizontal-lenticular at the
quartz and plagioclase phex ac s 2,
Small lithic inclusions are
Spherulites are visible in cc 1 'L IC
,
cA
L c,-3
The lowermost three
softer than that above and uTCc e :_,
often white or pink. The bc,S G octc, °o-)
W2 sec. 33, T. 7 S. , R. 20
V -t` o
c l1ll :c
dense, black obsidian.
aI
be
1_ V
ns
in the
o
J_0L. Ct.i..' ViG,F ,
to a
ti oen at tie root pass
ignimbrite seems to have iDeo
The
T e J v _i. C O.
on 'she
: o'U woe
.3.,
east of Clarno and in the
R. 20 E.
e occu_ J
Petrographically, the
varieties:
1.
cn ,
amorphous, cr15
Amorphous.
At many outcrops, the
posit did not crystallize.
ou
"b
r;o
vl
r
a_ vet o
._s
the de-
at at a
,;older.
Long streaks of
tuff.
lei to the lower contact
matrix
of shards
C3
sur2CJ
e
rc
(see F.
occur in the Mass.
Lar
r't
L...,
deformed but not collapsed..
Mass is 1.526.
0,"
On the beer
C 0
(17, p. 365) and Daly
D
the glass should be that
60 per cent.
rs 1.
o r I I-I
itof
t
r-;3 $ D
Inclusions of
always present, but few in
0(%
Table 7, number 4.
Crystalline.
2.
Unlike the welded tuff>. c):C ,elE
of the Clarno ig;nimbrite ci 6.'( _l_
oa
!,:1
due to its more basic con ov:e..o
crystal growth. Latent her; `.
crystallization, with the
probably prevented rapid coy.
In plain light, thin se
the same deformed shard and
layer.
Under crossed nicolee,
juxtaposed spherulites in a
mass (see
Fig.
17 and 18).
central cavity (vesicle?)
Gcn
r_'C
of tr_ amorpt fa ?s
I one L
'
r
Fig. 16
Photomicrograph of Clarno ignimbrite.
Deformed glass shards
and pumice fragments, lower zone.
35 X, plain light.
Percentage
of Clano
Constituent
Glass (groundmass)
Crystalline grounduass
(spherulites, quartz,
plagioclase)
Glass (inclusions of
pumice)
Quartz phenocrysts
so
Mid-andesine phenocrys ts;
Lithic inclusions
Apatite
Zircon
Tourmaline
T'ridymite
Magnetite
T = less than
G%
Explanation:
( 1)
Near top of unit.
R. 19 E.
(2)
(3)
Mid-unit.
Mid-unit.
(Li)
Bottom zone.
()
Segregate.
R. 20 B.
?.,
Same loca' i.
River
load
Cove C_ »,:>_-
11
A
Fib. 1(
Photouiicrograph of crystalline
A, lava fragment.
Clarno ignimorite.
deformed "shard" texture of round-
mass.
C, collapsed pumice fragment.
110
111
a low index of refracterminated, clear mineral ha
tion. It is either tr'idymite or cristobalite.
Clear, fragmented phenocrysts, up to 3 mm. in size,
of mid-andesine and partially resorted quartz are present.
The plagioclase is usually without zones. Lithic inclusions are predominantly of an unfamiliar, coarse-grained
lava containing quartz and plagioclase.
Modes of this
rock are given. in Table 7, numbers 1, 2 and 3.
3.
Segregations.
A lower, poorly defined zone within the ignimbrite
found at the road junction near the center of the SW-1 of
section 19, T. 7 S. , R. 20 E., contains an abnormally high
concentration of quartz and timid-andesine phenocrysts.
Some specimens have the outward appearance of granite.
A large slab, one inch thick, was found in the stream bed
that parallels the eastern border of section 34, T. 7 S.,
R. 20 E.
No other occurrences of this material are known
to the writer.
The rock is well indurated, breaking through ppphenocrysts and included lithic fragments. Weathering of the
groundmass causes the larger crystals to protrude, exposing
the hexagonal bipyrac;ids of beta-quartz.
The ground.imass is uniformly fine-grained and is
composed of anhedral quartz and plagioclase. Scattered
through the ground-mass are clusters of trid mite in
112
patterns that suggest a deformed vitroclastic texture.
The phenocrysts are so abundant as to be in contact.
A
strong force (presumably from the weight of ignimbrite
above) has crushed them in place so that a force-
i;
Zircon crystals
1.c
,
up to 0.1 mm. long are unusually abundant. In one thin
o-_-ben U atLi-on can be seen (see
section, 362 were counted.
beyond counting.
.
Apatite crystals are numerous
A ;-node of this rock is given in Table 7,
number' 5.
The loss in volume upon fusion of previously expanded
pumice would result in a relative increase in volume of
non-fusing inclusions.
The concentration of "heavy"
minerals however, suggests that gravitative differentiation
has also taken place.
Very low viscosity and high tempera-
ture must have prevailed in the mass for an unusually long
time.
Why such conditions should have been restricted to
a few localities is not understood.
Clarno Upper Welded Tuff
A reconnaissance survey west of the town of Fossil
was undertaken to establish more accurately the strati-
graphic position of certain rocks in the mapped. area.
It
was found that the Clarno-John Day contact lies at the
upper surface of a welded tuff two miles west of Fossil.
Fig. 19
Crushed phenocrysts in segregated
50 X, plain
Clarno ignimbrite.
light.
It overlies Clarno red tuff f and is overlain uncoii o ° . d o.L
alt formations.
the John Day and Cole::,.; t
t
The welded tuff ha._
was traced southwestward
N. 40 E. In the northeo
a_c ne
of 50 to PC feet and
,.a
e= along a ,Uri
fo
corner of the
overlies the spherulitic lava described
is
2 no
is overlain by John Day t
Two miles southwest of
"window" in the NW
of
a1
.
basalt.
it reappears in the
t-,
..
7
r
CODO
20
r
- Tere
-
it is overlain by a se21o
tuffs.
A small outcrop
0
of
NW 1/16 of section 344.
T.
to he,
co1"o(
W. ,
of Fossil. It c.on o m<
overlies Clarno igninbi its and i. We youngest rock of
lated with the welded tuaf w
Clarno age in this area.
The fresh rock is
A s been used
._o._
as a building stone in hU:-v'a
has altered
,i_
a
r __n tint to the
._U_._..p
some of the glass to chlorite.
outcrop. Area, glassi CO2 u_o ". oaa crust is found at the
__
surface of the welded tuff
i
tae
sect )O 1,
<:
T. ( S., R. 20 E.
vit .roclastic
The unit is charac
texture.
and
The shards are onus na
r;
many resemble sponge a ..,._Ci
_,
h
weldedt;
delicate;
+ape
t 03
in the fused margins o°
formation of shards adj
shape of many vesicles nc cat
crystals of tridym ite are au
_
ly near the middle of t ;
oligoclase occur in small
include tuffaceous sandstone
ignimbrite. Modes of sa
are given in Table 8 un?=-
e
11
.:_
r
C,i
051
f7 Ct
_ .e
si.
e
li l".,, no
outcrop w
Percenta
v
e
e
Constituent
Glass (+ devitr°if ica i
.u"! thi c fragments
rld-andesine
Oli;oclase
Quartz
Tridymi to
Apatite
Zircon
I'ria_; ne t it e
He ma tite
Chlorite
iiontmorillonite
T = less than
Explanation:
Clarno Lower +Ielded
Clarno Lower W elded
Clarno Upper Weld ed.
Clarno Upper Weld--U
Clarno Upper °eu.dl n
"c.
johN
t
...
Iv
`.Z
occurrence eon
i:.. c _.
Thick sections of colonel
V
Day formation are ex o
The best-known
outcrops
C
v 0_..
".,`
Day River fr om 1a1' 10 to
localities include the
0(1..
v='
no v %fi
-_.
ia_
f onurnent-Hanilton area cc the
jo h n
any scattered exposui:esl
system east of 11 ene
basalt
1
,
_
-1
1.L
,.
ho y
tuff beds north.
locality has been des_ r
The John Day force
i
ccc '. n t
Tertiary f orr,ations of
the amount of time
re qu
:'
not
.
known, and time-equ i va
very few of the major 1 Je i1 _L e
a
6)
made to a "John Day lake
description of the tuf
bT
him,
of volcanic ash, mostl
rhyolite flows.
e c:
r'ee"n, c;n
wer e, according to
He inc,_
L IC;
t,b: ee
woe "iN
Merriam in 1901 (28; .
lower red, middle
!
.
C 'i_
.1, C, U
on into
11
i _.- 0
stratigraphically above
"Colu,;bia lavas. "
i.G_. :o
J_'_
unto
L
..'_bee
1
the Clarno tufts at
CIe-
Bridge Creek fossil tlv_,L,
In the Clarno Bas '."i,
tuffs contains Bride Crc k
_1
co
dOtIn DJ
L
o
to r;
like those from Picture Go e,
tural features character ? ', ic:
i ossilti
a.:c.
v_
U CT
t
Vc
0
J_ a it
c
U
Jo
J LC
i
Day localities.
)C'_
Tuffs
ler o sees cc-
In general, John
crease
in clay content our.
.-c1
aen `_se as tuCV;
c', >e
are traced upward in t1 au
up of red-stained clays
l;- to
Leo:
a.
s,,;_
colloidal state in the
probably the product o
°e
r
sh, bet no
,all Tisolit'eo of
vo ca 1. c
trace of pyroelastic toutu
unknown origin are cons ors.,
r
a
or
of
brecciated during slwT 0
o'Ao-.
a
ally,,
.flue Lilicken-
sides.
The fossiliferous, 111J.i_ , ccO on,
of highly indurated tuff tunic. L,Lc e_.v
Creek, and on the sout'
Is
e'-1i
2
_L_r-i,-_)D
i
t
'- .ou
:iv ten
lRa
e e.'k
c. and Cove
T. 7 S. , R. 19 E.
U7,
Chalcedony is the main
oe
horizons.
01'
i. c.
gypsum, transverse
'ri
:el tox s
cc±
bceu hou ?c! in pie leaf-bear
tie fo
The larg
almost invariably rep
13 k`.
ys uhe
tL? ':i' arlr
t,
1_ce e U a
chief hardening substar
small fresh-water fish hia
L:: SUiC 1
C).O,r"T..!
..
u,;,Jc._,
1
i
. eves a
ow., 8 ld ty::l
ac
v
.r,c
r11F to
visible
to tie hedd.i'ng
cen ,.
section. Limonite occur-, up hO
tent is very low. Cthe,_-
C1aa; cow
c
size is too small to ue r.:; _
The green tuffs
toan the
lower beds and are colorr_d, accc
Cot
p. 82), by an unusual coi; L-_, nc ..r_on o
o- 'e
compounds, believed
of reduction.
1c
.viiait;ert
to bl- due to an
be inter
cuffs rr;a,
Light brou:i-c! a .rid.
(12,
.rya _:1
bedded with the green;
and crudely
stratified.
, a"::eni
of pr:r _c
sue alas
shards are often visib:.l_e.
Welded Tuffs
Early descriptions of t
"rhyolite flows." In coot
has shown them to be welded to1''s
include
-'"
the Clarno Basin, two such.
part of the section.
Cu the v,T si;
c X. a't, inaLUlo1
,
l2
23,
tale u ,penimost
3lo',era of I' 0 r! lountalrl
to
and in the slumped areu,:
UL
{.i
.
:)
,
,T
of welded to
fras,ments
profusion.
cl
The lower
out In ,rie Aria
_z
0
of The Cove, dust below
the "window" of section
both units
T.
are found,
a t- e,
20 E
L.
b,,-`JO
of b °ow
ce
"C' to 70
,
John Day tuff.
The lower welded
t
.c coi
e ,
and
1_,,,n x 4 ,
shows abundant compress d
pumice.
The lower tl i
welded.
Fragments of ot"ner 1oc o
this zone.
c :.
The unit is
._
r}
a -cd aoorly
opt c of l on on
1-1c
it is almost identical, oo
o,v
of
:)a 1
_
ho
welded tuff member of tc: e 21 _oca-uc
observed east
of the
Q ,a
'
Microscopically, t-_e
blebs of glass, 0.1 to I. U
strongly compressed and c
the long dimensions of
around inclusions and
_L c o
-
eQ
a
Quartz
is p :c
tuffaceous sandstone.
lavas resembling
C
i;_
the Cla r:.o
_
100 a._
a,
!u
v<a
a,
cc
C
1
y.c i 1I'i lUQ
O ',
index of refraction of
rhyolitic composition. lencc
andesine.
r.,
no
la
`s_ca-uI.._I;e
of
cllc
re mid-
however,
inc 1' unions of
onl:,
is
es
,
dodo
til c;c:/ioris 0000'
the bottom zone show the
different texture,
a
inci
r
abs
smaller and largely undo
surficial melting.
mucin
on]
f odE
9, numbers (1) and (2).
Several samples of
Ys=
similar to that of the
surface float in John Dt
R. 19 E.
Inclusions
ants in
of rots.
of small feldspar and quartz cy
a
of defor
type of resorption is diu;"i
An isotropic substance, probe
penetrates crystals of to
by a groundmass
resemble intergrowths
as
were
a
matrix
held to. e t1;er
a.
An unusual
0.'.
coysta_s.
c
4
a rtz on feldspar,
'v0._:As .'cLi
c granite.
o
Extreme granulation did not occur
the t.lo ri10
segregate, but heavy accessory mini.
Want.
Its composition does
not Lpeci Ica
to either of the known coan i)
this material
j f units,
of this rock is given in Table 9,
The John Day upper Aelded tuff is
high degree of welding,
Ann.
bottom are dark to yellocc.
visible fragments of deformed pumice.
ecc
Con the t
s yp and contain
C
o
Lc
f TI'S I'I
.Percenta
1_it
-
i,a
!L)
-L. 1,
e; O'
John
Constituent
Glass
Andesine
Oligo-andesine
Lithic fragments
Spherulitic interg°ot_L
of quartz and field.. at
L,
;
;
Quartz
Tridymi to
y
Zircon
Apatite
T
Rutile
Epidote
1'
1
r3,
I,
m
1
,
1
T
.,,
Hematite
Limonite
Magnetite
T
T = less than i%
Explanation:
tuff,d -n
(1)
Lower welded
(2)
Lower welded tuff, bo
(3)
2
Segregate? The Cove.
Upper welded tuff, cit-uini lt. :S c. V, 'i. '( S. ,
R. 2G E.
Upper welded tuff, top of uni ,. Same location as
(4)
(5)
R. 20 E.
e of unit. .lace location as (1)
9
11-1
ruidd_le are composed o-='
structureles s glass.
In thin section, faa
is iO';]{i an
undeforued vitroclastic
nigh degree of weldi
the groundriiass have d.ev..J.-
s . .'v 3
a:I
probable quartz and 1'e-16
Lar;e inclusions of
vesicular cavities are
of the glass is 1. 325,
.'ccv..0 i
Phenocrysts are nredolil _:
Jcyc' ,a
andesine and are clear,
often twinned.
of
Minute
colored variety of her: a n L
the rock.
T
The middle an:.
a
only traces of a vitroeL
na
ut
been fused into a base
a
tiY1oa
YS nave
C
pended clear, angular
'C'
e
U
odes
compressed streamers of
rock are given in Table
is
J
i 11
Thickness of the '
directly measurable.
fc
.r,..,,
not
v1_o
c'.
,
ate,
c
-_6
=oj
1200 feet along the Jo h
1VW and
n
feet in
jou
The Cove, diminishing eaadward
r octl.
normal
Because of extensive
o_t O
sequence of the John Day formation CO badly deranged.
Red tuffs with white straamo
occur only tear the bottom
of the section (see Fig. ?1).
Buff, ,,__o._, and white
be found anywhere.
tuff ape con-
predominant at the top, while green n
Good exposures of
nd - tu
fined in the Clarno Basin.
ti c
±..
below Miocene
Dow
con.. or
basalt where the two
able.
a:..'e
't 1 n
They dip three de
part of the area, and one to too he
Cove. Since the structure of the Olarno formation does
not conform to that o
s :e to_ uo bia
River basalt, and.
since the John Day tufts pinch out between t leo:, an a1r` L
unconformity must exist neap the bet of the John Ds
formation.
Slumping does not
peool. t
direct
a lion
of this at Clarno.
uc.t0
e ano
the s
The influence of ni.:
appearance of the John bad tuffs near Clorcio is remarkable.
:_uces internal coThe presence of water in the clays
hesion, causing them to
n -e as if nb
were a liquid of
very high viscosity.
C
...
of
a m na tlDn of nuff's
.
suggests too
complished along innu ;erc'-
:a_-i
slumped areas
displacement.
movement
,
The most obvious examples
ove 1:;e
bia. itiv
of John Day tuff involve t
basalt.
of the
Even without the
John Day tuff moves
th as little
o
slowl
exposed
tia.ca l cc f
eight degrees inclination, host of the john Day surface
romeo.
in the Clarno area is ch aracterizeu
_1
with small swamps and
lake-fill
Eroti io e..
_ocis.
basalt bloc s are widespread. The
John Day River has cut its bank into this material at
remnants of slumped
several localities downstream from C? arno.
hundred foot cliffs of ccc
Two-
boulders
of Columbia River basal
to ten
Fig. 20), show the depth.
W;ch maus ;novel nt occurs.
feet
.'oadci'.i.A: west of lla_ no.
Similar features may be
The two best fossi-,
a
(NA sec. 19, T. 7 S., it
an
tt
nox Ran
the
loco.
so ba
22. T. 7 S., R.
. j .
estimate of original position can
N
sec.
.;
.ntacost''
but
slump 4
seem to be from the core
fossil leaf
tt
oS
(sec. 20, T. 7 S., R. 20
Another
diameter (see
in
.
ecti
•
-
•
•I,.•'•
_.luI.
-
Fig. 20
Cliffs on John Day River composed
of slumped John Day tuff. Note
large boulders of Columbia River
basalt in tuff.
Fig. 21
Lower red John Day tuff, sec. 19,
Note white
T. 7 S., R. 19 E.
bands displaced by slumping.
occurs in place only at t ho
found as float throup ioM,
er
of limited value as a
of
_e
ctio
is
fhus
ad.
im se E5a 5
On the basis of the ur:
tEtc
Lower Oligocene Clar ,--)
ti g thick, conf,..
overlying,
the
Middle Miocene flood
formation in the Clot no
and Lower Miocene.
green
tuff
°oCV,
V rt
__°.,r
fos
john o:
f tuffs
.r,
in The Cove
down-
river from Clarno have
many years, but no profe
The above age ass!
from other sources:
'soo_°ted.
nce
z_. s n
t
0,
Cha
Creek flora as lower Jo
by Clarno Basin stoat
it is probably Upper
by vertebrate finds
(12, P. 30).
disputed.
The
Kate
=+_
-
o-_
ins
Some w,_''-! Ue:;_'
e.'
(30, p. 173), while of
E
Dc U 1,
Loyal`
Miocene (33, p. 83).
p. _,0-k3) recognizes the
c.1
on
jL o t`WC'-
Miocene and Upper
-inc.
K.
it
:10
C
in 1>1,
fossil evidence for '.` lon2n liont.
cal Society of America conmittee on
Z;
he Goc__o,_
continental Tertiary
_._co
correlation of the No"r't4.
e
t the
confined the entire fornation to the Upper
_
e
.
,
Upper
Oligocene and
l
the lowzr
of in
Lower hi'oc
_.
(49, p. 1).
L iv'i oni
Lithology of the
o'1 indicates tha-v
volcanic
the material accumulated _ _ o.
can.
A western source
served color
oxidation.
sequence
This could nave
C
aridity, brought on
one
scaue
i
bar rr°ier, or from an in--
in- the effects of conc
,..__ t
-_, v
oL
cot co cr
it con isted of
ha Y
wide, flat plains seO.
parallel, moderately
John Day tuffs are thin or
and attain their greor_ ;t
This distribution is not due
j
4 aatne
The John Day lands
one large lake as some
A 1 lI
ro
01,',
C_
t oc:
inal regions
_r:
6
u
.°no
n oar
od
synclines.
n ._. ob _on;
out stratigraphica l
def ormitive features
a. rr
aa;
inferred that sore of
folded Clarno rods
hinhs
e
o,
o`
non
oz the antic1=.no
oao
c
co a
ior", -
lands of that time.
The lack of coo
older rocks is not tie
tin 0
deposition are consider -Ga.
.J..
ably accumulated alonl
oho
manner as the upper
-i-c.c.
CIa u-no
o.-
f« I
I y in
Ponds and small
lakes
r,L.'cf cc:.
['..
.,he
belt, but after find n
el'.I
duou
6,
these forests to those o:
Metasequoia oxide ntali
ea''v
'(
?'':;.
temperate forest cove?'eoi
'v?ei_
c71'au.
Of 1 .-"
t1ne --ace
ave Thin-
bedded and contain old-,---
internal structure was
,ode of
a'L _o
)
113
co,, pared
!ode2 i-, Cal __Ii, ortIJ_a
ed4ao,od
c : oj_c
(no::
mayor
Iivn
.ca-
)
Metasequoia glyptostroi:,o _c.ticc,
cer,;_ discotioered in
Szechuan Province of Chi ia,
element in the entire
The upper mer;Uc
lo_
u.: ,. __
were formed by meat ato=_-.:ti C'
successively over t--his
_
o
f1
o:.ohc.leou
^i_c u t
=i1e
co ich cr pt
in their wake. Erosion,
leaving thick deposits of fine
e
even on the highlands, was p2obat
pace
<
__
with the rapid deO.i iaii scd :elit,ci t_i 0i,
Near the closing o
john
the Clarno Basin, two suc:,.solve
)
y.:ar
in
c coef do
eruptions spread
over tie.
glowing avalanches of cot
tuff surface. These solidifies as
.e
possibility that the t k O,.
. c ons_ le
deposits may also have been the
c:
THE,
oe vce
or these
of
remainder of the john Day formation should not be overlooked.
A$JCLT FOE}
COLUMBIA RIO
I.
C. Russell (32,
"Columbia lava" to
V
2Q
_.
.-lc
Washington in 1893.
1
7
U1O
d
.L
AMA],-
detailed
.2000
r s a' Eocene to Pliocene age weree
tl J_a `, ca:;
',t o"tl,y - shown that
__an (28,
included in his definition, i' >ccord:L.
:L.y,
,_
p. 303) restricted the term "Columbia : ` va " to hi c 1
sections of Miocene basilt alon, the Columbia River, The
post-John Day basalts at the Clan no 3asin may be traced
without interruption to these localiVes. Known general!
salt for io n, they comprise
as the "Columbia River
one of the most extensive volcanic formations in the
world, covering large pants OC Oregon. Washington. and
,t
n
Idaho.
c c e<
Phy
O
Oo?
basalt in the ri la _ no Basin forms
gentle to precipitous wargins.
highlands of low relief
Columbia River
L
:ions are
not well developed in this area because thick inter -lava
soil and breccia horizons are l<ackle .
The broad erosional terraces oomuo 1 in other
,33
-
_tt1.U.tt c
The upper few feet O
highly vesicular with a ti=''i c :'U.st
some instances, especial
I ow br CCia.
G:
lod,'
V
section, separate flows
Pillow lavas were
o-fcen
_i_nitti,,r-1-d ua l
a
he
o
G
cn.__ffacul t to dis t, niJ;uis i.
seen in h to to
flow of
on 1 oun-
ta in.
,er her black and dense.
iii.: vesicles of sO:ie I GL'j`
t: a in vu-.
contain -olite,a,
Our L C.J,.a 1.
Ll ill (.: lli'.'i[iO11.
this
The fresh hand specime
Phenocrysts s are
L
S'c'..CiG;:",
t
S-
on the south si de of L- -L
calcite, or chalcedony,
weathering colors the roe
L
t
b
No deeply
'_r
_'.
weathered flows were enco
uta
Seventeen successive
were examined
in thin-
_ cc
T,
e
-consist of
alec unite
magnetite, and traces
4.eJ
pci-i-sez_
cons and
up to 20 per cent in th
es
M ot s:.<
stitu'ce 80 per cent of h= o te- sup 'a ce
to 2 c . -_n
e 1 a locles
contain a few phenocrysis
ezo.°rb d and ;E:a i. zoned
length. They are mar
.
i ',
over a range of about
each lava
sheet, consist ry
a _:_
c
inwardly from a glass;, , e .__v( tar G.
li.c
= oundmaSS of
iocl. e, grades
c;: Gv:
no. iDe loc,
to a me ium-grainecy (0.--!
described
.yes t
brs
as subophitic. The seventh flG o a
i n v er.... .%
o a1t
n,-,..: G i.
texture. If the
a mount
ot.
1Ci ;1 jJL'+:3on.oeo
of olivine are usuall;''
--r o rois Of
saponite after olivine, occur o Lh 1. J1 er' J_ii'd s. The
ula
saponite usually cotta ins
L'{ Ge
?'!shne ite
.r
a 11,
.
G
mar pros G
crystals oriented norm
Nontronite occurs as eoi
of glass-rich samples.
chlorophaeite
Uh`u' pseuO.onor ;h.
masses in cavities
t rat_ on .:. n "gals are
Otl" e
after
and ch? o r_ ite ant;
after pyroxene. An i ,ve e _
in a -,undonce oe-
ort=} .__
'c
L
its
nd the ,' e u t e r a o_. °cc;. ,.U U:
deuteric origin.
Interbedded in the lacs+._ of 1 c ALoc T
tween glass
11
,.
i
_
mass of Columbia Rivet
:a ,i
boundary of the mapped
in the extreme
u.,t o f t'
a rid
north,, es"t_, car L'1
feet. Most of there e
s-,c-
c
:,-L
sa
it 7tonc,
and
e
u -k
o
ro
Co
em:'nen...
.
onion
cv on
sc
v
e4
shale.
Cree
a can
=:`hr
monol: t
` i L CPU
(
r.ioa,th
Quadrangle) and at sevrra!_ n
of Iron Mountain. A _im l .r
12, T. 7 S., R. 19 E., above
vary in thickness fro.;; JU'
a
t-. e
e,s`i catral
_i_",
of white, tuffaceous sa_ ds stone,
shows less prominent l a;<
a ri 'ns ve
sediments
ma t
In thin section.
a,nd to ne is
L:
o posed of u
,
.'ofi
lava,
ly coarse (C. 5 - 1 mm. ),
fragments of fin -`?,rain
32 per cent of the roe
U
I
contain angular grains of A
tals,
er than fragments of'
plagioclase lacks
1L
so',r
habit of granitic roc's,
Clarno lavas.
The
as.
au
up!
of the
The coy;
and constitutes 45 per
form skeletons of d.
ice o !:0
ca t__ tior_.u
c
are common.
_vn;
-non in Won "ou
Total thickness c
feet per aver,',
taro is approximately
flow, The observed ra n
fey, ,
,;-;lck-eW._
of the formation incressas to 120i :e north of iron
Mountain and decreases to
'o
a
1.
of The Cove,
This
variation is due to accAnnated erosion on the uplifted
eastern portion of the Cl no area.
J
The Columbia Rive
northwest through iron
_ iO!, n
ta i
ant one to two degrees
northwest in The Cove.
structural slope is sec
until it meets the
Coil
C
ha: ._°,u :-°1 re U-'3 0
No clear-cut evic
4_1
_L
o he
L+
-1,11
th
1 U,
'0V- I _ a l C
1.
oiCC1,_e
io: of fa
,S
Cat
Oii.
! e 51v_`T i
basalt was noted in the C
Columnar
jointin,_; oco
.
_ ,-,
section; elsewhere the
L",
4
n6
cc,1'o.
o
0
consists
ice irl oeals
of vertical splinters 11 -ic _ 6,_-
t ransverse, undula tin;: i
the
_c
a o G w:e .
CL°
e
rhho
pIaL
Jointing was observed.
U3 h J
Slump blocks of
The Cove and on both
Clarno.
corner of 6 oe a
-o Jpe
wY1:E
h L 1w
from the undisturbed
f1'
C
It
o
.; ana
'
va
UO
ai"0-:en u't
< nd.
roved on l-
3? Et
of
.ca -le
OU
the
Id's
sections.
t
n
covers ,..ore than
oed1y
t7a
a
-
_IUCC vertical feet on
''
in s truC t ur e a n -
Clearly, in
the river initiated a
tuff from beneath the
se .
'
a few hundred feet
s ha
dive. o,ell)`4,7
e _oci of tLLis type is locaib-ed
four square miles end. LOU
the eastern side,
'r;asolt ore co, _r,on in
of see Jo1- .E)
sj_()e_S'
One enoriuous
extreme northwest
_
olo °'
d
,.. t ofi )a io
The Columribia Riv,ie_
It has not been
considered to be Middle 'ii-'Locene in
dated by fossils in ce ` ra
stratigraphically between Loner i
ra c e ted
C
t
Upper Miocene Mascall fJ °;i
all
c_
anti
_ac
C)i!.`
Exposed basal contacts o_ the Columbia R ve_
asa i t
in the Clarno area indicate that the j_L.st John Day s fact
tore e ` oil Inu..- C [lave
.
d
was a relatively r.t: oo tl l
f
preceded the lava floods
ca us
o `e
ce `' a in it
egu-°
larities in the contact an
John Day upper welded tuf
t st rea r c,han .el and the
s ve tv discontinuous.
Because of the side ... a. occurrence o basalt bike's
he direc , ca send.
in association with flood bass
som et- mess been observed.
and-effect relationshL _sch
between them, the lavas are believed to case sued. from
_
it
long fissures rather than _oca1. 1.zed poI.,.a rs. No feeder
ut a r orth.-sol h complex
}:ea
dikes were seen within
in .cr ,1;,_tte Cree<<
of multiple basalt dikes
r
canyon, 8 miles north 0}f
The first flows
the Clarno highlands to
ring molten floods sp:- ao.
T--,-),,
I! on.
e
OS
)
oun e
a._r°
vs;
,u
e v=tiers'
a1 f,
nv da e
a 4 mos
= Wren
RecU'Yr -
.
en
a
re
0U
surfaces, covering lake,
patches of soil.
The
erboddec
sediments and pillo
on the lava surfaces
absence of preserved call
U
5
,_ti
not due to their removal
short intervals between
thickness of soil on
the intervals could not
mi lleniurns
0? n
U
and in some
A
years as ample time
0
the flood basalts at
than 200.000 years,
10,00(_
O_n:_,
oa
P
_0
e
OL
PLEISTOCENE AND RECENT
Although no poi
-Coy.
;'e >c
formational status exist
widely distributed sedt
age merit discussion.
ocks of
captain
Cla
rcc _._ oce i
o
J
and Recent
fall into three
Y
Pleistocene Terrace
terrace
sediments formed under the
_
deposits,
influence of ice age ci
th
volcanic ash.
1.
Pleistocene e
ueve8
a
Four hundred feet a: o
on We
01)
homoclinal ridge southeast of ;l
gravels, sands, and sllL
rocks in the bed of the
CA ape siallap to
n
.:god
occur at the same level
oection 22
cea
and on the surfaces
z2.
1_.et1
formed on John Dad to
have ceen
Ot ue
notable terrace locals t1_
lower Bridge Creek V
the mouth of Meyers
Gorge.
Hills
een
Canyon. and
Merriam (29,
skeleton of a Pleis tueWt.
of these terraces.
The Pleistocene to
where preserved from r .ce
vary- in thickness fro ___l
U
are s.
ce
,
_cial and,
erosion in thE Cla± o Basin,
or
he
<
<
c upper slopes to
twenty feet near the sl-
ne d Vo its
structure may be sec
contain serpentine, sao,c,
a la id
L
C I a. n
other rocks fore
pebbles predominate on
much of the material V,1a
2.
Stone
,a_
' ow
Rings,
Deposits.
A strikin cha ,, c 2
salt surface in the l
_ve
o
_ __
stone nets, rings, and
of angular blocks of
arranged in patterns
slope.
7c1
Polygonal or ci
e
ground, becoming elon-r .,:,C
slopes.
These
feature,
ar eat photographs oecau :
.,
eat s'
n to
0e
L:;:_-
avT;a:'?
cantor o. e cn rang conjlcaJns
fine silt, allowing
While there is
mode of
origin of these;
erally attributed
thaw.
_C0SI-I
I;L
to :ho
As the rings
o
t. o> are g;en-
k
e io a a.
ti
vigorous activity of
winters in the area couoo.
io
,-ovi
c Ca.
r' e c z e and
Fig. 22
Areal photograph of Pleistocene
stone rings and stone nets on
Columbia River basalt highlands.
(Series DOV-1H-107)
1 442
interpreted as the result of
the seve-i-e climate which
existed during the Pleistocene.
On these same highlands, associated d:itl:h the stone
nets,
is a discontinuous
and inconspicuous covering of
very fine, light brown, silty soil which seems to bear
no genetic relationship to the relatively fresh
on which it rests. It is interpreted as a thin
of Pleistocene loess.
3.
Recent Alluvium
basalt
deposit
and Volcanic Ash.
The alluviated floor of the John Day Valley in the
Clarno Basin varies in width (torn approximately 100 feet
to C. 5 mile. Similar deposits are found along Currant
and Pine Creeks. In most instances the deposits seem to
discharge, at he ;o the of tributaries, of the load carried :>y flash-floods. in places
the river was shifted against- the opposite valley wall by
this process.
In a few localities, notably in the center of section
2, T. 8 S. , R. 20 E. , and on the road above the _ it ve_r in
have been derived from
section 23, T. 8
S., R. 19 E. ,
protectec
volcanic ash have survived erosion.
roc Lets of white
The ash is th icker
and more widespread in the southern part oat the quadrangle.
It fell in recent times over much of central Oregon, being
rapidly washed into creek beds and depressions. In many
1!13
of the valleys near Mitchell, the ash occurs in white
layers at depths of six to twenty feel in the a i! u J Lim.
Its source is not certainly Y,_no n.
GEO" ORPHOLOGY
Phys _L
l_ C
The landforms of the Clarrio Basin are i, idly con-
trolled by structure.
cua acte_oized
As each fO_'mar _c l1
by its own structure, it is app °oprriate to C`.e cl.rib e the
physiography of each formation and to regard- f o national
boundaries as the boundaries of nh .iop aa:h _c a aprovinces.
The hills underlain by `paddy Ranch ;.k
ur
_.._te have
smooth profiles even though t icy have steep sides, narrow
summits, and are separated by deep rave. This is due
to the homogeneous character of the rock an to an unusual
type of weathering, described on page 13.
Because of extreme inequality in rock 'hardness, nearly
al of the Clarno formation in this a._ea i in steep slope.
ons are
Ridges and summits are sharp and angular,
generally deep and narrow, and valley sides are irr°eular.
Flat-lying lavas are sculptured into benches and mesas,
but lavas with moderate initial or structural dips commonly
produce homoclinal ridges. With feed xcept_io Is, intrusives
stand in relief above surrounding rocks. is'_edf low units
offer little resistance to erosion, but
form high
cliffs where they are or recently have bee protected by
overlying lavas. Good examples of tLiis are the
145
i'n sections
vari-colored cliffs facing the John Day
3 and 10, T. 8 S., R. 19 E., and the Palisades of section
35, T. 7 S., R. 19 E.
John Day tuffs have been moulded into compound hand-
f orms by the interaction of fluvial erosion and mass
movement. Most of the tuff surface is cn.aracten: zed by
hummocky ground with small swamps and iaue-l'_Llle - depres-
11nlless the tuffs
sions between blocks of slumped
_roc :s, the.,; do
are protected from erosion by over!,,
not form steep slopes. In some parts of the John Day
valley and in the western part of The Cove, em !ants of
smooth strath terraces are easily r see-`l.
They are strongly
dissected, but a reconstruction would show a broad surface
sloping in a quasi-hyperbolic curve to ra.:_ d he river from
the tuff-basalt contact on both sides. Tile lo'7vw potions
of this surface were in the approximate location of the
present river and about 200 feet above it. Unlike some
regions upstream from the Basin, only one terrace level
seems to be represented.
The Columbia River basalt underlies smooth, rolling
The broad
highlands with gentle to precipitous ra
upland ridges are locally incised by d ap canyons.
Erosional terraces cut from successive flows are present
but not well developed.
146
Process
Most modern erosion in the Clarno Basin takes place
in the spring and early summer during large floods following storms.
A given stream bed may contain running water
only once in ten or twenty years.
But one flood may
accomplish as much or more erosion than would uniformly
distributed rainfall during the interim.
Upstream from
narrow water gaps in the valleys, flash floods sometimes
deposit ill-sorted alluvium over large parts of the valley
floors.
Ordinary erosion may then cut deep trenches in
these deposits, falsely suggesting rejuvenation.
These
features may be seen along Pine and Currant Creeks but
are more common and better developed in the Mitchell area.
The importance of slumping as a geomorphic process
in the Clarno Basin has been emphasized in earlier sections.
Whether or not it is active at present is difficult
to demonstrate.
Downstream from Clarno, tall cliffs of
obviously slumped John Day tuff seem to be actively moving
against the river, but the river may be undercutting
static tuff (see Fig. 20).
Roads built across the tuff
in pioneer days have, to the writers knowledge, never been
displaced.
One sees no evidence of uprooted trees or
deranged fence lines.
Most of the modern features of
slumping may have been produced furing the last stages of
14
the Pleistocene, when the climate of this area was presuna bly more humid.
Direct gravity transfer is
por' a 1G i
man
locali-
ties near the John Day River v;her_e tall cliffs of Clarno
As
ove._ yi=. 1 a uas.
mud low deposits are protected
of udflc- sediments
the caprock retreats, large
(as large as a
small house, ._ 30ii?G`
spa:__.
the cliffs. The blocks dis n t
a' e
are rare.
b
The Palisades a.v
tom.
Several very large mudflow blocks
-fell
}
`
r OM
tales piles
this.
a
Pine Creek
p otecValley during the writer's field seasons,
Al l
tive lava cap was thin and underlain ;per cthat remain are three small i';e ::;na lts one l e to the north.
`he.i_r
Stat
An understanding of the geomorphic history of the
Clarno Basin is essential to a correct -nt,re pre tation of
its modern multicyclic land 'orms. This rlistorut is inseparable from that of the John Day River. Portions of the
John Day Valley above and belo Clarno c aich have been
through them,
cut into the Columbia River ;asalts
;ea;:dering
display the sinuous pattern of an i ltrenc
stream. The pattern does not survive on a John Day tuff
the rive._- Crosses th . I Cl eeeIlk antisurface, out
{rd
;
cline (upstream, from Clanno, see u. if) it has been
a{
48
superimposed from Columbia
River basalts directly onto
Clarno rocks, preserving some of the nears: e- rs.
The intrenched meanders have been i ntere_reted by
Hodge (20) as follows:
blocked
central Oregon
Construction of the Cascade 'mange
drainage, creati
in which Pliocene sediments of the
Shutler formations were deposited.
Condon Lake"
Madras, Dalles,
and
An eastward-eroding
stream in the Cascades tapped the risin lahu waters,
forming the Columbia Gorge. These events i to rated and
exp!anarejuvenated the Columbia drai aie system.
Lion of the intrenched meanders of the Desc-,utes, John Day,
and Umatilla rivers is that "after Condos ra s was drained, the above streams meandered over the al,i flat lake
beds. The falls and rapids of the int-c° nc
;:streams
followed necessarily the course of the raeendt s" (20,
p. 70). In certain respects, this is inaceouete
explain rejuvenation in the '.itchell quadran_ le.
Meanders developed directly on the Columbia River
basalt surface prior to deposition of the I=1,iocene sediments.
Hodge's map shows meanxderr, patterns on the Shaniko-
Condon surface (a relatively, undisturbed
j:
.c oral and
basalt surface of north-central
Oregon) cut into pre-Pliocene rocks that rise above the
as the high ea t level of
1900-foot elevation set by
topographic Columbia River
Condors
Lake.
They are also 3ror
: nr nt in tD Mutton
Mountains region which, because of its h_L iii position (20,
p. 50), probably was never coverrred by the Pliocene se.di-
iile not as
i;ents. Furthermore, intrenched L,,earide
as
well preserved, may be traced up the Jo n Dail. re cuv into .'(J ..L tLia v are
far as Kimberly, where t
,'
3000 feet in elevation. In coy crast s no m c d :;_'s a `e
seen in areas now mantled by the la e r c`'s 01 in certain
other areas where their past
Clcauno aus:in
The mode 'n features o:i oliel iin
have been in process of fo a'c on since the late T'<'LOCene.
It is probable that the Columbia River bass It;; ,,ere the
last important rocks deposited and that the once covered
the entire area. Consequent read s gay" la .re developed
L
_
11- ID
'
meanders simply because of t1-.-- vast extern;
of the lava plateau. Whether Cond.on rake
Flu.
J o4n f-i'adient
>_stea or not,
the Dalles-Shutlei° sediments are clear ._a l teat
conditions were unfavorable for re uvLnatio o iE
Cole bia sy-ster, until at least lace. PIioceme t_nie. 1 he n
it did occur, the superior erosive poeeeer of tale Columbia
River created an inequilibriwuii in %,rade v' ni t1 sent rapids
up i.ie is sno ring
and waterfalls migrating, as H_o'Le
in
occ
tributaries. Late Pliocene u p l t ' J '
t
the Clarno Basin in accordance n to areas to Cio east,
nation;
but was not a necessary factor in thi
c
: ' ti
(
150
also strong-
the relatively undisturbed 3haniko surface
ly rejuvenated.
A broad Pleistocene :i:loodpla_n ex tend--,)d ,%ith minor
interruptions up the John Day Valley from
mnt six
miles below Clarno at least to Picture
It formed
of temporary
,within the intrenched system
and marked a
base leveling. The floodplain i.%a- widee on John Day tuffs
where, by undercutting the basalt clip'? s,
°iver°
destroyed its former intrenc cent att e_°. The ancient
floodplain has been nearly obliterated. by a second rejuvenation, forming strath terraces on John Da tuffs and
isolating patches of gravel on high river bluffs of Clarno
rock (see p. 139).
John Day tuff is the moat sensitive indicator of
in the Clarno area because it is a pas, _ e participant
in valley development. It is unable to :.;, = i iuv ose a
roc s. It responds
stream pattern inherited frog: oven
quickly (in a relative sense) to minor, teim,p,or'ay _'I uctua,
more
tions in base level, not sit ni-' icy ntl1
resistant f ortm)ations. The position of secondary drainage
akness in
channels is largely determined by st enbtn o
Cove Creek has
nearby, overlying rocks. For example,
-
11
----e
caused a recession in the extent
of Colt,-'-
a Rive
basalts
in The Cove which exceeds that caused by the John Day
151
River in the northwest cor'"P. y o
E'S:.
s variation
is a function of thickness
the basalt e and is l the
affected by the tuffs on y'rhic.? the c_w
developed.
=. Fe :'N',
Late in the development o
pla in,
sa
f 'a lures
it is likely that the John Day
of old age on the John Day fore ation,
the valleys on
i,
C arno rocks were mature and the
,'1, 1
highlands were young.
,ul! r:;.,'_
Lane-i ores of re c
_
subprovinces display youthful characters.
o -c
a alt
in in these
-t e smooth,
symmetrical profiles of the strath ter,.aces .p_ear to be
profiles of equilibrium, and as such indicate that the
f loodplain and its streams were at r°ade.
i e fact that
some of this graded surface has survived recent tuff
dissection is a prime example,, of
.mma.tur _ty
in the present
erosion cycle.
Because of the inequality of : oc': har'cness, a youth-
ful stage is probably short lived on Cl arno rocks,passing
rapidly into maturity. A well irate prated dra inanee sti s'cem
is characteristic of the Clarno subprovince and has
probably prevailed since its erosional dis.nternment. It
should be noted however, that many stream near the John
Day River and the river itself are not in
trelt with
Clarno structure and lithology. This is due to superimposition, probably from Colurn via Liver .L,asalts. As
152
,minor changes would in most instance
justliments,
the Gla..l.ad-
co -.-- ` c
a youthful stage O1 erosion in these areas is
indicated. Rhoads Creek, n i ch dr°a ns ;o s o _ :'. 8 S. ,
R. 20 E., has excavated a large upstream basin in soft
Clarno tuffs. Its only outlet is thro l a :}arrow ravine
in Clarno basalts. Under ad iustmen't co 1C7- , s the` creel-would have shifted down-dip to the nor a s't, re:ovin:
j(, -
the overlying rudf low unit. Tee, now occupies
Yits to lard
is position passes suddenly from
lavas, undercutting the verb: resistant black OCR int
live. About one mile dOwnst eam, the John el
into a
cut
avoids a hill of soft mud"!:lO'.
large Basalt intrusive. At the mouths ow ay _ otto n,
Spring Basin, Cup-_.ant, and D -y Greens t...:. .lard lava
which these streams flow could have, been ate
J._ L
sections
s1...J11 J shift onto soft t:iudflo-n,
9 and i6, T. 8 S. , R. 19 E. ,
mountain of hard lava U ithou
-ravel on the nearby low-lev
upper reaches of creeks in the
r
tea
leav=_Y1
of
Ver
c
The
=a0
.cone a t, well
rea are,
adjusted to rock hardness.
The Columbia River basalt 'highlands
consist o
poorly defined inter stream,- divides
V-shaped valleys which are :._, ,endim_ thems
ward erosion. Geomorphic youth JLs obvious
road,
Y_ar,C'Ow,
yeti
_..
_e.
b,.
head-
153
Areal photographs show numerous recently abandoned
river channels in the alluv_i_um of the John Dad,' Valley.
These features are preserved upstream from Pesistan-c;
obstructions in the river bed, Some of the old channels
are 20 to 30 feet above the river, showing the extent of
recent downcutting.
It is doubtful if the John Day Rive_ is now being
incised as rapidly as in the immediate past. Temporary
base level, as far as the John Day tuffs are concerned,
is to longer determined by the Columbia L River basalts
downstream from Clarno, but by Clarno bearack which is in
exhumation in the northwest part of
the first stages of
100 feet in
the Basin. The river drops approx
its 20-mile course through the mapped area. No waterfalls
exist, and rapids are confined to gravel tars, ApparentY,,.,
the erosional emphasis has shifted from incision to valley
widening.
154
STRUCTURAL
The Cretaceous and y ou_ to
are involved in a regional
folds and gentle warps.
r
oL
of
note;.]
:.o
'.o
La sin
est
ou
ne
One of the
he
this system is the Hay C'eek_
Clarno Basin is situated, or, it
r; r..
:c'n
4e
The thick sequence of CrE taceons
surface at Clarno probably, fo rreason
21 through 24, dins about 31 d gees to
o_,
.
4-
=
following the outlines of a Qr e-C-La o'no
In the
_
,o`..;
a wedge
,
is < "enate,
The ti"1i n ed?e
Basin this edge lies in the su sur a
It
os on al uncor_-
.
1
pages
vest,
or°i
c
is bounded above and below u angular and
forreties. It probably for i ;S, ? n erase o
thickening to the northwest.
below the
.1
here between
.
Clarno and Muddy Ranch.
A sheet of Clarno rocks of variable
i:'des t limb
northwest
of the
until
Hay
it
Creek,
ine
a
approaches the
r
slight upwarp occurs,
structural terrace.
A
s_L
rah 1
synC
..i..
iU
a .L
t
J_ C orno a
[C ul a vi ii
L
1i° 1--
probably exists just west of Cliarnk--,,
..,..
C c;
-
v
1A
limited (see Fig. 23). In the i'udd Rc esi
formation has been sharply folded into an. a
_ort east-
a
:'
i,
a
on. the
ceyreea
....i_L
i
southwest line through Clarn0
._? c Irc-L-t-
as
'J .4_ks
io
R
WD
s
data are
thee Clarrio
etr'ical
Fig. 23
Outcrop of Clarno rnudflow conglomerate
on John Day River, sec. 5, T. 7 S., R.
Eastern dip suggests a sub19 E.
surface syncline in Clarno rocks between this locality and opposing dips
near Clarno.
anticline which
northeast,
Us form ano r l' o ,'
ton
Above the C l eroo, .`oh
e- ,
thickening to the norW
n john Day andl.
representing the
Clarno
rocks dur'
MY!
the northeast par, of
MO.
elsewhere by erosion,
surface of the 1
folds.
ion
tuffs.
to
not
el
the 015.5:]
eew nor
Dip is 2
Columbia
Day
__' a Jl _ .. 'i.
ie
. Lru
The,..
to 3 degrees no.
uz: _l
surface co
tit
C
one
__d1 e6
.;(1.,., _iko surfs.
of north central (I=
The above
Web
S
into existence
p cession which ,.L,
Tertiary.
Die
1_
__1
t__«sc
°o_
t i, 0 ::.'.h the
oi
of
the
-i
the Cretaceous
the Lower Oligocene.
The
former vemoved
from central Oregon and crat
folds; the latter
tes
of Clarno vulcaih ci;.
e
__
ti
55
..,_e
ypoootypes
i0
lent
Columbia River
time, but probes i
-._
oc
_._
c
15
Fig. 24
Nearly horizontal Columbia River basalts
of Iron Mountain viewed across upper
Clarno dip slope of ignimbrite. John
Day tuffs between, pinching out to the
right (east).
accordance
(see Plate
..ne
already exl3tent,
The
little 1_'ese
tJ
They seem to
tectonic
to 00a
a. nC.
Mons.
'aC
t'u _;
Faults
the accoYTp«n;
pai ticulai
a. '_D U. , n
0,' _Ii)
Gnm
1 .P 1U rocks,
o
..
_>
everywhere
-. a ti
'.,1. _ .
Fa
! Q,
large eno '._.-.
one
exception, an
oCL ata_on
east-west
krona.
ii '-
CODU_
basalt or
.9
R. 2 .1-1
0 1;
ry
111.0 rno
Mainz aw
['w_ ,.___.
,
..:
__-
1-,
,_..-
.'._.
t
W- t
_. -/u1 _
.:.
,
Pre
known,
-
i-LI
deposited
1 oc1ci jr
of
pe
'
v
1A
__._
[ a -jr c t"'
C
They were
_
processes,
):'_C
t
_L'o:n
formed an
a
CicL nta
prevailed st
div., °s fled.
.:;0_.
this ocean.
deposited
3;
i
')
source WG
Die
causing rapid W.
of eruptiyc,
n
M-
in the AV
..
i,a te
_
lJ,
UC
pebbles.
d into
westward,
the proto t_
today,
t
M
oo
retreat
conglomerates
this gay,
J
._..:tc
7
the C.t. lIIUr'[1Ci
Y_j
nce,.
Durin some
.LAG
(_
Eocene,
The Sea ao,_,1.
top
-L)-,O
=i 0
El
_DO
08
C)
.., .
:..
Cl :.t _.
dissected
couoaped the
issis an(--
co'oespoi
7
_-.
eruption
r
GJiGC
ciuti_ a[_t._TT
W
so
u
intense and
C
unable to
was
noveent
tonal
OOaceous ..oc
rocks poured
low elevs
Earl
-L
nudflowu,
After
buli
apes,,:,;
veryneKed.
c.
abundant
CMS,
o;''
L
l1`
t:_O.'1
Co
faces between
fosnilo
often?
roxinatHy
accumulated. ac t .L
canli
feet of
these
broke out
1:aC.l1liJd:i_
bac
and southeastern
w s --._>-
canoes eru con e
va..:i_c t
mediate lava.,
sequence of
They
_ac:,(.
t1
G
n
of
cis,
t1_
a !. U s y
=
l. ed
a
s
it s hO
a second
for
9
c
i-
`
C
.)c _ce t
C
e
s
coy
h: t the .,lama
000.
vd i..a
io>°
HO
n
processes, the
.s
c h o he r>
.
1a,.._-ned
_
Basin was probahi,j
ate sediccu
,
_t t t..._
.. over the ,!.ol'i1.O
:J u
intermittentiv in
.
and w.!
ioc_ of volcanic
rents, and out roe
stra t`! gra
_ _...a_..
i'a0G
o,:'6
Erosion of val
area.
ge V'ol-
a as,
ef-
the
Od,.._
ra
ociactic
A reduction
accompanied the e;
further mudflnt, I_
Basin was
,,n .r. -_ _. _
ash which a'c;t
to
PD
u,
volcanic
__
tod so slow
a
_
faster.
in the as__ bets was b Oct e
oasons the
11 OW
resultin;
this way,
at it wac vitered to
some place
e
probably
UW-
L
laterit i c 0 la!
the lower half
Near Cla
c, -_ c
tc.
served,
N
layer i
t[i.. _:out
.. C.. _.
v
been a no
oo o ) ._e aJ ._c1te
x t`.
._.
eruptions of the Hai
At the
covered much.
_
un,.
c e3
o
the topography s _1
this curl
esait flows had,
Ql
so
_.
e o.
(
meandering sty
W
odaC v
other mammals,
.n
forms
>
u unid<<_nti
a
lied.
During Log.. u_
occurred nine
hot, e ' e '. 4.
1
1
73
the plain,
steam.
`(-
Cove
o
lJ
material. coa_le
:..U..
After a-n
WE
in the 3a..,=._.
The
i':,:_
Cretaceous
diast r
oDr.
,
defined by
_
:)l..t_
.
a,....
.....L
', l c _ no
the Nay Creek
anticline
produced
:_ y nce _
no:
lam? a rno Basin.
were
.al
tJ
.
. ,.-..L v_
in (C
0
Minor "wrink!
o U Of Cove
tun 8b
0 the ail",!,c
i:_c:L and
Creek
lei:
At C _e...
durinS W,
poW
2ty(.iGt1,._
Ranch.
t:e o .,
Cut into
1." 1 mbr tE-.
0Ct
dust began
and
vejon hill
ell
.ow1.a_
tuf fac.eo
o: a o
and pond
oak, laurel,
less tropical
_o
L
were po
I 10
evolving
is
oi:
',:7_L
C':
a_i
drifted
with a Pall
climate or repe
Ve
_0
CA"
way to op,
animals
C''.
which the
..
1"o',,,
3
e
se _
of ore oaons
vo en; the
the rains of
30i
tracts
ma j op st o_
of clay
,;:
0_
cen
010
en
mclinal lowlands an,-.,.
No
e, but
v_i,
almost buried the J_'iv, C.._ _ i a,, :I_
. fall, two _) successive e rupt_ ., z
fore the ..;:1 had i".oa.`:it. ,. '-'.,
_"__n .
_
h
c ., r
1.
Oi We
so
C1drno
as
ei
Lan z1ass over the
ALY eviconce of local
marked contra
volcanism
Mich was
to the type of volcanic out
During Gooc,
L
o
ad
basaltic
it
with ne a i;- 100
:
:` i0
,: e
_
of
ti
_u
,.:_
tuffacacus sediments be-
-
r.)a ti
iJ
W Go
are C0:1,
rough, barren au
7val of
time
short,
in
Pei
e2i
the Clarno region
eo :10100
.. _ o and
fore the next
between soc::
of
lake 6evel
lower Butt(' Creek to
on the second flow
the
01
. ..
probably to
River
o
:'1
'j l ..T
c _1
1t
.
the
o
MU
ac.
over
a n c 1.
,
to _t.Jf feet of f20 15 to
which was underla-L
MIA
25 sheets of lava,
probably covered.
No
later rocks
in the area
The
consequent
roe a_on
CC,
<-
.. ;o
-
that
a,
_op".u on the
+
0 scene,
level plat
existed until p
caused, in all 1 --
Fat
_i
tion of the Oo
up
the core
deep
cot,......t=,.o
s
ni)
ODWOMT
tie-known
,
_a R
of
ens -
.
c
I
jo
31
v,l-v'
_`
'1
Li
canyons
als
The
ssaa.
surface in
level of
00
t above the
surface L-_-
difficult
accentuation
physiopraeh;
now
Mko
a necessar
n. was
7CAL H
nay nav'
decrcaE-
increased the
d Lt in
During
e._.
b o. _.
achieved, End
Day
channel.
where erosion ..Jl::_
Colon
_
the
._
icy
'_ a
meander
015
t at^ ll..'.
l ..s an
ot_
Cloy,
of
a -.
An indication
.
the C burld
1.`;
G
-
north and
By
I
Pine CreM
C vi
River baaalt
LF,
area,
John Jai tV
level, .._ e t:
erosion ha
Cc
Since
of a semi-arid
from early
ci.ona ]. un
age
10
__.
seasonal
_.
narrc.v con;
streams
1't
41
The
C
times as
quickly
exists toc
3
ti,
_
:.
The
i_._a1..:0
V!
chiof
Basin is wrte-;
t
Creeks,
i
and
contact.
.7C))
N- ea_
J
Cont olle C'.
or-_
J
at -heir
inL.
J...
Poo
tut a CeO)
in'
(13, p 23,
between
C U 11 _L e
o
idc
Dn:,
A similar
creek ('n
has 4'Tai rPx,.11
i..
70n_.
The
C1ari o
_
writer, ha;-;
At several
asphalts
as
0
small
T
pC
unusuaii
)_M_
._ j
i
L!.
o a ,.
Vii.
_
yi
d
i;i,
_
1°3
they
we ve
without s
in
J0 (10 1,
,-,
i__
1. c...
_
ra
: t
., ion
of volcanic dD.
C
tillat1o*1.
With
this
Me d in he vol
was
_'_i.CC-i. t,iA'
of Pine Creek in
strata were an
structural Uap
well to be
terrace,
rj', nt
Na c
__
3ed
te_ published
(25
OP surf
r ta
sit i,G ou.
U
J
.L.ende.x.
to
abandonment
drilling in t
a structural
of further
to
tanvacc in
a_
Because of
;:he
i.nuerir-r='
1,
,<v.at:toy.:i,.ic
+-
any
have its soorca in the
Cretaceous rocks, Even if
y contain oil. which is
doubtful, no structurc with sufficient closure co tie
Vious Strata to
it in commercial quantitina, nor
petroleum in
he area
runt
,
cap it, is likely to
i;
o s.nr
.
in the C_
a
this
which showed
respect
;.n
4-25C fees
0uu
-.'
'1o Basin.
I29
WALIOGRAPHY
Anderson, C.
with
Califoonia
r
of volcanic We
T_e
..
"u,
Univerni
G uD.
Pubilee`t,
2,
Lend
_
__e<a
Bedf or
0 a. U
Mitchell
Corva i
.y
Jo
{
.
ate CO-1
e
..l
numb.
leaves.
3.
4.
1f o. n.1..,J_iJCj
Bowen,
0,
BoG1re
A:
_i od
of
"1G. iJ
511.
_LO
. T':.
1950,
me e o a con
,
n
0o;_ vs :_l_ ,
vicinity,
ty..
thesis.
.,
152
5,
Brown,
Natural HIM03,
1954.
6
7.
o f to the
CUM
of the
Publications
Chane,y,
(
Cal ..i_. or n
109-172.
t
Creek flora
Institute
c
8.
Cr
uoo
.us
-'
u
.,
-,..-.o
.
_
o2is
.
Q
50:1-22.
V ion.
Pen
1935.
Oregon.
9
i
,:
Ion,
n State
O}
s guilt
Lecture FuOlications
lc.-onL-o1C' ,Y of the
10.
Crooked 1.,_L
e_.
_Loc
_
Bridge Creek flooc.
Publication
a!
._ ,
C' :, .
to the
titUtC of Wasting=
1 1
.
Cochr°an, D. e. &Azestad correlation
C. nozo c ,
eastern
io _in: Field
chart for-
crayon
Oregon, Dapawtmen
of
Y
de. cot.
__
and Mineral
'7
Ineuot
Bulletin
12.
Coleman. A,
e._',
Gorge C
=wall ... Oregon
13.
Colliep.
of
the
Da 1
,
c
.-,
ec
"__
15,
10.
earth.
R. I.
Dana,
lot
3. and
ships
;'r
J.,
17.
New
>98 P.
A textbook !lof.-
York, ..i' e- , 1_54,
anic relationSelected
Geological Society of too
at
Memoir
1933.
_l __,
iau E. Ford.
s'J il
mineralogy, AN 26.
Emmons, R.
t
)Us DOCKS
New C
.
rxey al _ eso:tinc s
d
Bureau of Pines aQ
Oregon
Geology 1(3)`-,14.
as
1953.
George. W. 0.
of the natural
parties
1(012 L .__c i o
;12 ; M... ses
to
ci C0O3osiIIio
t.. r ^ .L .L
Journal of Geology 32.353-372.
con of mountain build!
( i11oJ ,, ;0ve;
in geologic
c Ga.:.
Bulletin 60:56
O
.
C"-
of America
Society o1
.Jl,
-.n
C:).i:ii.c! ..e ..Cito
vus.,y 1.57y 19juI,
19.
Hancock,
1959.
20.
Hoe c, Edwin T. Geology of north central Oregon.
State College Studies in Geology 1- 7 . 1 42.
Oregon
21.
Native . a3phalts
Association of Petroleum Geology _sts
22.
Howard, Con°L u
;1L'a.,
American.
HAS, 192Y.
on.
Butte area
G olo
step ';,-,
and V 1.0 __ ,.J .
thesi
Co_ al is. Oregon wtan-_-, Col
955.
nu:oh. leaves.
23.
_.18
i ish, Robert <.!. The Seololy of the Juniper Butte
thesis.
G°__
area, Spray quadvanye, 0i x'._;0::1.
''"
'
Cor'`aa_li
leaves.
.
Coo C o i State College, 1954.
t
Y3 numb.
24,
Paul A
i
Kc.L' '3
Optical
fcc
.__.i,_.ciu
P"cG°aw--
25.
1°aCkGyy D. K.
Clarciv Basin,
Oregon, Dc a
G:D_ 'v_ i'.1v1
t me
Bulletin5:1.11.
.
26,
'OpOZ'w on
..
Jhectc
of
.
marsh,
t
part of the
Cornties, Oregon.
Mineral indus
w .Joti __
the Rocky
27. MButte
in re
....
1.
journal of Science, id
_.. '.: r n
_ oL UU
i7Vr
y
1875,
Cii1t .i'cy _.
and v_!_,,;.,_i._t, ,
thesis,
96 nt
28.
29.
.
3,
C o2vall:._ s,
.
_i.
as
y of We 'l!a. s.ic!.i
_:01 i
! Its .._ -
o
area
l
csC vanyiC, _1"'O lvf':,
Stave
o
C
astwtS
9D3.
"o____c
.
l.)tito J;.1
john A A C'V1` br.v ,f1
Ii ,
the john Day
Univansity of CH
ca tions in Geological Sciences 2:2(01 through the john
.:_o_;
in.
Day _..
i`
11!e1r c]ia,
y
,.o,
L
30.
12 .'r 6-
; .
Ee 'r
john C.
....
uo of toe john Dw-v
on
1Orfl c foul
cie
_.
.
5:171-2C
O,
1909.
Feecc 1 do, j,
Now
u.
wowln i,.1
character of
interior or l__ UnItea
Vc.,
0a 10,:,
S,
-
-co:
,eon.;}
Sc zuJ to, 0.
,
Bull , t_n of toe
93:73-=- -;'9.
34.
Scott,
from
i
t
S
J
J-
a es,
0
c.
o..-
and
_
1949.
Eocene o!
w'_
a':
a __cC
H
!1
_a
`os s of the western
lDn,
,'"r'0
GC o_ oo_t a.I Survey Oil and
We sh ' l_"on.. U. 3.
1-108. _3_-..
33.
_1.I.i
of Ca _._
o
__
(L
t
1 90:1,
1. a1,1. i i
1 sheet.
C
c`3
ii.
y
944.
J_Y1, ev t_i_--
in central
108:
172
35.
os
_
of O.
Eocene Clap no
96B: 6`236.
fruits and seeds from the
G.-.
Fe _
Scott, R. A. and _ _ oo 3, He i+ot _1.
Cenozoic of .,e0 U
of Eul lea in
the
of (,ate
JouC'iia
.o
ArsU . mum, Hanv
?,
,
Gi t G
'c1! fiwc
The occurrence
0:i
or L America.
and University
36:259-26D.
37.
j,
Sc_ iveno
Keloet in
lee
astrowma
cal
-;
(li
a iL ; e
1929.
38.
Bald Mountain area
Snoop«,
and v-_cin__teo
thesis.
70 000
39.
40.
313 'v
i1-_u..
na
Eocene
2, 6,-7
J o_)
Swarbr
tooth
of Faleonto
Erno
'(sue;,
GeoloK
area and
v 003.
Maid ie r
41,
2
leaves.
St t t.or
102
1952,
_.
o
y,_
ciiii i .
a nd Ku n-,-,
V On,1
Geolo(:,
New York
42.
43
44.
Wa
vu:^ iSrO','i,
-
igneous
OWIVOP deposits of the
Ta t e
r.a_"
.
U. GeOlo '
Horse Reav
oica1_0ez3 or We1300.
Wi 11
Eugene,
Hi
-t.,
Higher
15
?w.
V'd1.1._ oec:
Gibe- ,.
06 o.
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