Geologic Framework
Introduction
Geology affects ground water occurrence and movement. Understanding the
local geologic structures (primarily faults) and stratigraphy (origin, vertical
sequence and horizontal extent of different rock formations) is important to the
evaluation of the ground water resource.
This investigation relies upon the geologic work conducted in or near the eastern
Lost River sub-basin by other investigators. Their work demonstrates the subbasin geology is complex. The use of rock chemistry and radiometric age dating
analyses by more recent investigations has aided geologic interpretations.
The general stratigraphy of the sub-basin consists of basalt and sedimentary rock
and sediments. Basalt occurs throughout the sub-basin as multiple layers with
some sedimentary interbeds between layers. Basalt exposure is generally limited
to the uplands. Sub-basin sedimentary rock and sediments predominantly occur
in the valleys as lacustrine, fluvial, and volcaniclastic basin fill that overlies the
basalt. The thickness of the basin fill can range from a few feet to hundreds of
feet. Some basalt dikes, sills, and flows are found within the basin fill.
The general sub-basin geologic structure includes numerous north-northwest
trending and occasional east-west trending faults. Most of the faults vertically
offset geologic units creating upland blocks (horsts) with steep escarpments along
the fault. Down-dropped blocks (grabens) form valleys between the horsts.
Physiographic Province
The upper Klamath basin is located in the transition area between the Cascade
Mountain and the Basin and Range physiographic provinces. The eastern Lost
River sub-basin is located within the Basin and Range province. That province in
Oregon is a small northwestern portion of the 300,000 mi2 Basin and Range
physiographic province extending into California, Idaho, Nevada, Utah, Arizona,
New Mexico, and Mexico (Orr and others, 1992). Generally, the province is
characterized by long and narrow, north-south trending fault-block mountains
separated by broad sediment filled basins.
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Stratigraphy
Development of Stratigraphic Understanding
Stratigraphic interpretations for the eastern Lost River sub-basin are becoming
more detailed with the aid of rock chemistry analyses, radiometric age dating, and
other tools. The greater detail has caused interpretation modifications over time
regarding rock origin and the relationship between rock units. Understanding the
historical development of stratigraphic interpretation for the sub-basin is
important for minimizing technical confusion or conflict among researchers,
interest groups, and/or the public discussing various hydrogeologic issues.
From 1950 to the mid-1970s, geologists largely divided basin sediments into two
units: recent surficial deposits and the Yonna Formation. Lavas were assigned to
a few units. The relationship between the sediments and the lavas was
problematic.
Meyers and Newcomb (1952) separated the geologic units into younger (upper)
and older (lower) alluvial deposits and upper and lower (bedrock) lava rock.
They described the upper sediments as water deposited lapilli tuff and the lower
sediments as a composite of lacustrine diatomite, stratified sandstone, laminated
siltstone, water laid ash, pumice, and semi-consolidated gravel. They noted the
sedimentary units included interfingering sedimentary layers, intrusions by basalt
dikes and sills, and thin gravel layers that produced small quantities of ground
water. Lavas identified were predominantly basalt or andesite with some dacite
observed locally at the north end of Yonna Valley. Meyers and Newcomb
reported the largest quantities of ground water coming from the lavas (flow
breccia, shattered vesicular zones, broken or porous lava, cooling joints, and
effusive cinders, scoria, or lapilli), and they described the ability of solid flows to
confine ground water to the more porous lava rocks as very limited.
Newcomb (1958) defined the upper and lower sediments of Meyers and
Newcomb (1952) as the Yonna Formation. Newcomb noted interfingering
between the upper and lower sediments in northern Yonna Valley, structural
influences upon the formation in Yonna Valley, and varying formation thickness
(100 to 900 ft in Yonna Valley and exceeding 1,500 ft in northwest Swan Lake
Valley). He interpreted the lapilli tuff deposits in northern Yonna Valley as
truncated tuff cones (volcanic vents).
Peterson and McIntyre (1970) described the regional stratigraphic units for the
basin. Units identified in order of decreasing age were: Oligocene or older dacite
flows exposed outside the eastern Lost River sub-basin; Oligocene to early
Miocene andesite and basalt flows, pyroclastic rocks, and andesitic sediments
with total thickness exceeding 2,500 ft; Miocene to early Pliocene rhyolitic and
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dacitic pyroclastics, palagonite tuff, tuffaceous sediments, and minor basalt and
andesite flows with total thickness possibly exceeding 13,000 ft locally; early
Pliocene basalt flows with total thickness ranging from 20 to 600 ft; middle to late
Pliocene complex of diatomaceous and tuffaceous lacustrine sediments, eruptive
centers, maars and tuff rings, palagonite tuffs, welded tuffs, and basaltic tuffs,
breccias, and flow interbeds (all Yonna Formation equivalent); early Pleistocene
basalt flows; and Pleistocene to recent eruptive centers and local deposition of
various sediments.
Illian (1970) relied upon Peterson and McIntyre (1970) but summarized the
regional stratigraphy a little differently. Rocks described in order of decreasing
age were: aerial dacitic lava flows exposed at Quartz Mountain; sands, muds, and
volcanic ash from explosive volcanic activity; thin basalt and andesite lava flows
(unit total thickness possibly exceeding 13,000 ft locally); basalt lava flows from
eastern basin vents filling erosional depressions to form the most permeable
aquifer (unit total thickness ranging from 20 to 600 ft); Yonna Formation formed
by lowland lakes filled with diatoms, mud and fine sands, ash from volcanic
eruptions, and lavas; cap rock lava erupted from fissures; sub-basin sediments
deposited after faulting created the sub-basins and rejuvenated erosion and
deposition; and pumice deposits from the Mt. Mazama eruption about 6,600 years
ago.
Leonard and Harris (1974) focused upon the eastern Lost River sub-basin as well
as the Klamath Marsh and Sprague River Valley. They combined units mapped
separately by Peterson and McIntyre (1970). They identified nine units divided
into three age groups that overlap (three units per age group). Three units
identified as Tertiary (Pliocene) age were: lower basalt unit composed of jointed
lava, breccia, and interbeds that forms the most productive aquifer (equivalent to
the lower lava rocks of Meyers and Newcomb (1952) and Newcomb and Hart
(1958) and to the volcanic rocks of the High Cascades of Moore (1937) and Wood
(1960)); breccia and tuff of volcanic maars (highly dipping tuff and breccia near
volcanic vents); and Yonna Formation deposits of layered siltstone, diatomite,
sandstone, pumice, gravel, and tuff primarily of lacustrine origin. Three units
identified as Tertiary and Quaternary age (Pliocene and Pleistocene) were: rocks
of volcanic eruptive centers that occur as an assemblage dominated by basalt and
some andesite, rhyolite, and dacite occurring predominantly as tuff, cinder cones,
and lava flows (Swan Lake Rim was used as an example) and occasionally as
dikes and sills; andesitic lava flows exposed outside the sub-basin; and basalt,
breccia and pyroclastic rocks that form Bryant Mountain and other uplands and
locally interfingers with the Yonna Formation. Three units identified as
Quaternary age (Pleistocene and/or Holocene) were: basalt flows that form
rimrock or caps valley margin slopes; alluvium composed of alluvial silt, sand,
clay, peat, volcanic ash, pumice, gravel, and slope debris; and pumice from Mt.
Mazama. The description of geologic units mapped by Leonard and Harris in the
sub-basin are summarized in appendix 7.
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Pickthorn and Sherrod (1990) and Sherrod and Pickthorn (1992) conducted a
regional investigation analyzing, dating, and mapping rock units in most of the
upper Klamath basin in Oregon. Their work significantly modified stratigraphic
interpretations. For example, eleven samples from volcanic rocks previously
identified as partly or entirely Pleistocene were found to be older, 6.88 Ma (megaannum: million years before present) to 2.80 Ma range (late Miocene to Pliocene).
They narrowed the age range of most Yonna Formation equivalent sediment
exposures to 5.5 Ma to 3.6 Ma. They separated previously lumped units into 13
Quaternary units (four in the sub-basin) and 17 Tertiary units (12 in the subbasin). Quaternary units mapped in the eastern Lost River sub-basin included
surficial deposits composed of channel, flood plain, marsh, and lake deposits;
alluvial fan and talus deposits; landslide debris; and sedimentary deposits and
rocks composed of unconsolidated sand and gravel, sandstone and conglomerate,
and diatomite. Tertiary units mapped in the sub-basin included three Basin and
Range basalt units included vent deposits; younger palagonite tuff; continental
sedimentary rocks; tuff and sandstone; basaltic andesite and andesite; andesite and
dacite; rhyolite and rhyodacite; tuff and lapilli tuff; and older palagonite tuff.
Many unit ages were identified as contemporaneous. The description of units
Sherrod and Pickthorn mapped in the sub-basin are summarized in appendix 7.
Black (2004), Hladky (2003), Jenks (2004), Jenks and Madin (2003), and others
conducted detailed (1:24,000 scale) investigations in and near the eastern Lost
River sub-basin from the mid 1990s through 2001. Figure 19 shows areas they
mapped.
Their work refines and further modifies earlier stratigraphic
interpretations. A synthesis of their investigations follows.
Current Stratigraphic Understanding
The stratigraphy reported by Black (2004), Hladky (2003), Jenks (2004), and
Jenks and Madin (2003) identifies multiple Quaternary surficial deposits and
numerous, predominantly Tertiary (Miocene to Pliocene) volcanic and
sedimentary units. The surficial deposits include modern fill, modern dredge
spoil, lakebed sediments, alluvium, colluvium, alluvial fan deposits, landslide
deposits, basin fill sediments, stream gravel deposits, and windblown sand. The
predominantly Tertiary volcanic and sedimentary units include numerous basalt
flow units, basaltic andesite flow units, basaltic andesite dikes, tholeiitic olivine
basalt, cinder deposits (basaltic and basaltic andesite), altered basalt, lahar
deposits, volcanic breccia, volcanic surge deposits, mudstone, siltstone, and
sandstone units, and diatomaceous and tuffaceous mudstone units. Many units
were identified as contemporaneous with complex relationships. Faulting made
interpreting the relationships difficult. Units mapped in the Bonanza, Bryant
Mountain, Dairy, Langell Valley, Malin, Merrill, and Lorella 1:24,000 scale
quadrangles are summarized in appendix 7. Correlations to Leonard and Harris
(1974) and Sherrod and Pickthorn (1992) stratigraphy are shown in appendix 8.
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Figure 19. Areas of geologic mapping in or near the eastern Lost River sub-basin
from the mid 1990s through 2001 (each rectangle is a 1:24,000 scale
quadrangle mapped)
Sedimentary unit depositional environments described by the authors include
fluvial, lacustrine and volcanic. Lavas associated with the sedimentary units
include subaerial over-land flows, valley fill, sills, and dikes. Volcanic unit
depositional environments are also described as variable, ranging from subaerial,
to showing some interaction with water, to submerged. Some volcanic units
described show gradations indicating they experienced multiple depositional
environments. Unit thickness ranges from less than 50 ft to about 2,000 ft.
Sedimentary interbeds identified between some flows came from various sources.
The vents for most flow units were not found.
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The authors noted the importance of water in the depositional history of geologic
units mapped. Many volcanic units show a water influence. These include
hydrovolcanic eruptive centers, surge deposits (tuff cones), pillowed and
palagonitized flows, and basalts with altered groundmass.
Additionally,
lacustrine (lake-deposits) sediments are extensive in the valleys. Dicken (1980)
noted a pluvial Lake Modoc inundated the Upper Klamath basin valleys
(including the eastern Lost River sub-basin) during the Pleistocene with a
maximum shoreline elevation of 4,240 ft. M.D. Jenks (oral commun., 2000)
found fish bones in the sub-basin, and I. Madin, (oral commun., 2001) observed
shoreline features and deposits outside the sub-basin. Valley floor elevations in
the eastern Lost River sub-basin range from 4,100 to 4,200 ft.
The sub-basin basalts with altered groundmass were described as basalt flows that
encountered water but maintained a basalt flow appearance, similar to Snake
River Plain basalts that encountered water (Jenks and Bonnichsen, 1989 and
unpublished). Exposed units appear to be older, weathered basalt. Buried units
appear fresh when first exposed, but rapidly decompose when exposed due to the
altered groundmass. This alteration can affect K-Ar and Ar-Ar ratios causing
possible age dating errors.
Some units show evidence of hydrothermal alteration or secondary
mineralization. Jenks (2004) noted altered sediments cemented by hot spring
deposits near Lorella. Hladky (oral commun, 1999) observed hydrothermally
altered sediments at Olene Gap. He additionally noted celadonite and zeolite
lining basalt vesicles in drill cuttings from well KLAM 52096 near Lorella. A
1999 downhole video log of KLAM 10362 near Lorella and KLAM 51131 in Poe
Valley also revealed secondary minerals within basalt vesicles. The location of
the wells and the hot springs near Lorella and Olene Gap can be found on plate 2.
The authors postulate that geologically young, Miocene age basalt exceeding 7
Ma underlies the sub-basin. Most exposed units sampled in the sub-basin dated
from 3.8 Ma to 4.6 Ma. Samples yielding the oldest dates were tholeiitic olivine
basalt from Bryant Mountain (7.33 ± 0.77 Ma) and basaltic andesite from Gift
Butte (8.18 ± 0.12 Ma). Tholeiitic basalt from 905 ft depth at well KLAM 52096
near Lorella yielded an age of 5.79 ± 0.12 Ma.
Geologic Structure
Exposed Structure
Many north-northwest trending and fewer east-west trending faults dominate the
sub-basin’s geologic structure (fig. 20). Most are normal faults creating tilted
horsts separated by grabens.
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Figure 20. Faults mapped in or near the eastern Lost River sub-basin (from
Sherrod and Pickthorn, 1992, Black, 2004, Hladky, 2003, Jenks,
2004, Jenks and Madin, 2003)
Langell Valley is bounded by faults on the east. Black (2004) noted normal faults
east of Lorella make three steps down from Goodlow Mountain to Langell Valley
where the total offset remains unknown due to the difficulty of correlating
stratigraphic units. The minimum topographic offsets reported are 600 ft along
Goodlow Rim, 1,285 ft along the middle fault, and 700 ft on the north portion of
the western fault, decreasing to the south. Jenks (2004) noted individual fault
offsets of less than 400 ft in south Langell Valley. She interpreted the south
valley as a half- or trap-door graben with the hinge on the east and the major
graben on the west (cross section 1 in app. 9). On the west side of the valley,
Jenks mapped faults coincident with Ralston Spring and neighboring springs.
In the Bonanza area, Hladky (2003) mapped a fault along the base of Short Lake
Mountain escarpment extending through the eastern portion of the Town of
Bonanza near Bonanza Big Springs. He additionally mapped faults within Yonna
Valley in preference to an anticlinal interpretation of earlier investigators.
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The Swan Lake Rim is also the result of normal faulting and bounds the east side
of Swan Lake Valley and Pine Flat. Hladky (2003) mapped branches of the fault
extending into Dairy. The topographic offset can range from about 200 ft in Pine
Flat to more than 1,300 ft in north Swan Lake Valley.
In Poe Valley, Hladky (2003) mapped faults in the eastern and western portion of
the valley, and Jenks and Madin (2003) mapped Buck Butte and other faults in the
southern portion of the valley. One fault mapped in western Poe Valley coincides
with the Lost River and adjacent springs. Buck Butte Fault extends east from
Stukel Mountain into Bryant Mountain with an apparent offset of nearly 1,000 ft.
Buried Structure
The relatively flat surface of the basin fill in the sub-basin valleys conceals many
structures. Some of those structures are apparent on plate 3 and in appendix 9.
Plate 3 shows the top elevation of units dominated by basalt and buried beneath
basin fill sedimentary units. Appendix 9 shows ten cross sections distributed
across different valleys in the sub-basin. The cross sections include projection of
faults identified by previous investigators and faults inferred on plate 3. The
limitations of plate 3 and appendix 9 include a lack of well-to-well stratigraphic
control for the top of basalt, limited well density, and variable information quality
from water well reports. Recognizing these limitations, several interpretations
follow.
In south Langell Valley, the geologic structure appears relatively uncomplicated.
A cross-valley, east to west dip to the top of basalt shown on plate 3 and on cross
section 1 in appendix 9 supports the trap-door graben postulated by Jenks (2004).
Northward, the structure in Langell Valley becomes more complicated. First, the
top of basalt elevation contours turn westward in the vicinity of the Miller CreekLost River confluence (pl. 3). The change indicates an east-west structure across
the valley south of Miller Creek, possibly an extension of an east-west fault
mapped across Bryant Mountain by Jenks (2004). Further north, an apparent
series of two graben and two horsts occur between Goodlow Rim and Bryant
Mountain along an east-west line through Lorella (pl. 3 and cross-section 3 in
app. 9). The horst locations coincide with locations labeled Lorella and Lost
River in cross section 3 of appendix 9. The graben locations coincide with wells
identified as KLAM 10362 and KLAM 10634 in the cross section. Hot springs
southwest of Lorella occur in the vicinity of intersecting faults apparent on plate
3. The fault between the horst containing Lorella and the graben containing well
KLAM 10634 intersects a fault along the east escarpment of Bryant Mountain and
the apparent east-west fault near Miller Creek.
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Around Bonanza, a series of westerly dipping fault blocks (faulted up on the east
side and dipping west on the back side) predominate the structure (pl. 3, cross
sections 4 and 5 in app. 9). Multiple tilted fault blocks occur from Keller Bridge
to Harpold Gap/Horton Rim (cross section 4 in app. 9). One fault intersects
Bonanza Big Springs. Structure contoured within Yonna Valley from Bryant
Mountain to the Highway 140 vicinity (pl. 3) generally support the northwesttrending faults mapped between Bonanza and Dairy by Hladky (2003). Two
deep, northwest-elongated depressions occur within western Yonna Valley in the
vicinity of Alkali Lake and the intersection of Highway 140 and Bliss Road
between Dairy and Yonna (pl. 3, cross section 5 in app. 9). They are westerlydipping fault blocks abutting faults on the west.
Data within Swan Lake Valley and Pine Flat are limited. A depression occurs in
western Pine Flat (pl. 3, cross section 7 in app. 9). Within Swan Lake Valley, the
top of basalt in the southern valley dips to the northwest. A fault occurs along the
western valley (pl. 3, cross section 6 in app. 9), and a possible east-west fault
crosses the northern valley south of Grizzly Butte (pl. 3).
Data within Poe Valley are also limited. A northwest trending fault mapped by
Hladky (2003) parallels the Lost River in western Poe Valley and intersects High
spring (cross section 8 in app. 9). One east-west fault crosses the valley in the
vicinity of South Poe Valley Road and wells KLAM 51131 and KLAM 14795 (pl.
3, cross sections 9 and 10 in app. 9). Further south, a second east-west fault
coincides with Buck Butte Fault mapped by Jenks and Madin (2003), including a
buried portion crossing the north end of a southern valley extension. A buried
north-south ridge occurs in the southeastern portion of the valley near Harpold
Road and the north-south line between townships 40 south, 11 east and 40 south,
12 east (pl. 3).
Age of Sub-basin Structures
Multiple hypotheses for the structural development of the sub-basin exist (app.
10). Before Black (2004), determining the likely hypothesis made assigning an
age to the structures problematic. Black notes the geologic data indicate the onset
of master Basin and Range faulting in the sub-basin commenced about 7 Ma (late
Miocene), and non-master faults commenced about 4.5 Ma (late Pliocene or
Pleistocene). The master Basin and Range faults produced the major uplands.
The non-master faults produced low-relief, intragraben horsts (small uplands
within a valley).
Sub-basin Geologic History
This history summarizes the geologic histories found in Black (2004), Hladky
(2003), Jenks (2004), and Jenks and Madin (2003).
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Calc-alkaline basaltic trachyandesites exposed on Bryant Mountain are the oldest
observed rocks in the sub-basin. They were deposited as thin horizontal sheets by
a late Miocene (7.32 Ma and 8.18 Ma) eruption over subdued topography. Some
flows show alteration of groundmass by interaction with water. Lacustrine
sedimentary interbeds occur between some flows. Field work revealed no vents
for these flows. The flows are assumed to underlie the entire sub-basin.
Basin and Range faulting commenced about 7 Ma. This started erosion of fully
emplaced basaltic trachyandesites creating low hills and broad valleys.
Faulting continued through the late Miocene into Pliocene (5.27 Ma to 4.15 Ma).
Lacustrine mudstone and fluvial deltaic sandstone accumulated in the developing
basins during a period of volcanic inactivity in the late Miocene. The mudstone
came from volcanic ash from nearby eruptive centers.
Volcanic activity eventually resumed and continued to the late Pliocene with
eruptions occurring along master graben-bounding faults and within the basins.
Andesite and dacite flows erupted onto the sediments in the north and calcalkaline basalt erupted in the south. The calc-alkaline basalts have two different
chemistries and a maximum age of 5.4 Ma. They erupted from currently visible
and buried vents and flowed into the basins and up against the basaltic
trachyandesite highs. Flows locally ponded and/or interacted with water over
large areas. Volcanism during this period created subaerial flows, pillowed lavas
and basalt with groundmass altered by interaction with water, palogonitized
basaltic tuff, hydroclastic surge deposits (tuff cones) and basaltic cinder deposits.
Exposures include sediments and pyroclastic tuffs interbedded with pillowed
lavas and basalt with groundmass altered by interaction with water. On Bryant
Mountain near Lorella, the tholeiitic basalts cover a thick sequence of interbedded
sedimentary rock and basalt with groundmass altered by interaction with water
indicating fault movement was ongoing during this period. Evidence of faulting
within the basins (grabens) comes from low relief horsts capped by basalt with
groundmass altered by interaction with water such as Dead Indian Hill.
During the Pleistocene, pluvial Lake Modoc (Dicken, 1980) purportedly
inundated the sub-basin valleys in addition to the Upper Klamath Lake and Tule
Lake valleys. The lake elevation apparently fluctuated rising to a maximum
elevation of 4,240 ft. During this period, lacustrine deposition occurred within
the lake, Miller Creek formed a gravel delta as it flowed into the lake, and other
alluvial fans were deposited by other drainages. Some geologists suggest separate
lakes existed in each valley.
When Lake Modoc receded, it left behind Upper Klamath Lake, Tule Lake, Alkali
Lake, and Swan Lake. Additionally, the Lost River was established. Subsequent
deposition includes colluvium, playa deposits, windblown sand, landslide
deposits, and stream alluvium. No local volcanism reportedly occurred during the
Pleistocene to the present.
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