NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
5
Tcc
Tto
Ttbc
9
Qay
22
Tgo
Tcvc
84
Qls
3997000
Tcc
27
Tcc
Tsb
Ttac
Qay
Tcc
A
3
A
4
Qay
13
Tcc
Tgy
?
12
Tgy
Tto
?
Tgo
Tcc
Tsb
22
20
Qay
Tccu
?
11
Tsb QTse
Tto
5
?
Tgo
3995000
Tsb
20
?
15
Tcc
3
Qtr2
Tsb
?
Tgo
Tto
18
Tcv
18 Tcv
34
29
74
?
54
18 22
3994000
Tcv
Tto
Qtc3
54
2
Qrg Tto
Tcc
Qao
24
15
Qtc3
10
3
Qay
Qay Tcc
3
Qtr1
Ttbc
7
Qay
7
3
Tcc
Qtc2
Tcc
Qtc3
5
Tccu
6
Qtr2
8
Tcc
Qtr2
13
10
12
10
4
Qao
Qao
Qtr1
12
Qao
Tcc
Tcc
Qtc2
w
Qtc1
Ttac
w
w
Tcc
m
b
w
Tcc
Qrg
b
Qrg
Qtc2
Qrg
Qao
4 Ttbc
Ttac
15
Qao
Qao
Ttbc
Qay
6
Qao
Ttac
Qrg
7
Ttbc
Qay
10
Ttbc
Qrg
8
82
Qay
9
Ttac
Ttbc
2
9
Qtr2
9
Qay
Ttbc
Qtcg2a
Tto
Qay
Qtr2
3
Ttbc
?
Tto
?
Tto
Ttbc
Ttbc
Qay
Tcc
Ttbc
Qao
AM
Qay
Qao
b
Qtcg2a
12
Qao
Qrg
Tcvc
Qay
4
Qtcg2a
02'30"
58
18
1
Qao
Ttbc
Tto
Qao
Qrg
3
2
80
2
2
2
Qtcg2b
5
AM
?
Tch
Tch Tcc
Qtcg2a
Tto
Tto
Ttbc
Qay
Tto
Tto
Tcc
?
AM
Qtcg2b
Qay
E
Qrg
Qtcg2a
E
Qtcg3
8
?
Qrg
Qtcg2b
?
Qay
?
Tcv
Qtcg2a
?
?
Tcc
4
af
?
5
3986000
Qtcg2b
Qrg
Qtcg2b
Qtcg2a
Qay
Tto
Qrg
Qrg
Qrg
af
Espanola #1
Ttbp2
Ttmp2
Qay
Qrg
P
Qtsc3
AM
404000
405000
P
407000
02'30"
B'
1
0.5
0
1 MILE
A
A'
LC-r
LC-s
(White line, circles, and type)
CHIMAYO
0
1
NEW MEXICO
1000
2000
0.5
3000
4000
5000
6000
0
7000 FEET
1 KILOMETER
?
?
IIIIIIII
CONTOUR INTERVAL 20 FEET
ESPANOLA
CUNDIYO
NATIONAL GEODETIC VERTICAL DATUM OF 1929
Magnetic Declination
September 2002
10º 16' East
At Map Center
New Mexico Bureau of Geology and Mineral Resources
Open-file Geologic Map 70
QUADRANGLE LOCATION
New Mexico Bureau of Geology and Mineral Resources
New Mexico Tech
801 Leroy Place
Socorro, New Mexico
87801-4796
[575] 835-5490
This and other STATEMAP quadrangles are available
for free download in both PDF and ArcGIS formats at:
Mapping of this quadrangle was funded by a matching-funds grant from the STATEMAP program
of the National Cooperative Geologic Mapping Act, administered by the U. S. Geological Survey,
and by the New Mexico Bureau of Geology and Mineral Resources, (Dr. Peter A. Scholle,
Director and State Geologist, Dr. J. Michael Timmons, Geologic Mapping Program Manager).
Geologic Map of the San Juan Pueblo 7.5-Minute
Quadrangle, Rio Arriba and Santa Fe Counties,
New Mexico
http://geoinfo.nmt.edu
Tto
P
P
4
P
3
Qtsc2
Qtsc2
5
Ttbp1
LC-c
LC-d
Qtsc2
IIIIIIII
?
?
IIIIIIII
IIIIIIII
May 2003
by
Daniel J. Koning 1, and Kim Manley 2
New Mexico Bureau of Geology and Mineral Resources, 801 Leroy Place, Socorro, NM 87801
24691 Ridgeway, Los Alamos, NM 87544
Tcc
Tch
Alcalde tuffaceous zone
Tcv
Tccut
Ttac
Tcvc
Española tuffaceous zone
Ttbc
Tto
Pojoaque white ash zone
main coarse white tuffaceous zone
Ttap2 Ttbp2
Ttmp2
Ttap1
Ttbp1
Ttmp1
PENNSYLVANIAN
*u
Metamorphic Rocks
YXu
m
m
b
b
Basal Alcalde tuffaceous zone(?) under Black Mesa (ATZb) ― A thin bed of dark gray (almost black), volcanic lithic grains that are
equivalent in size to fine-medium sand. This was initially correlated with the CLTZb tephra, but the grains are darker than those of
CLTZb and more like the color of the basal Alcalde tuffaceous zone in the Chimayo quadrangle to the east. There, this ash has an
interpreted age range of 9-10 Ma (Koning, 2003).
A
A
Fine white pumice west of San Jose (FWPWSJ) ― White pumice about 0.25 to 0.5 mm in length with less than 1% mafic minerals. 9-20
cm thick. Age unknown.
Española tephra zone (ETZ) ― Dark gray to light gray, fine to coarse basaltic ash that is locally mixed with minor sandy detritus. South
of San Jose, this unit includes a basaltic phreatomagmatic bed 120 cm-thick, which fines-upward from lapilli at the base to coarse ash near
the top; it is poorly sorted and many of the tephra clasts and grains are discolored and altered. The coarseness of the phreatomagmatic
deposits strongly suggest derivation from the Lobato volcanic center located in the eastern Chili quadrangle. Based on discussion of
this tephra zone in Koning (2003), this tephra zone probably lies in the age range of 10.2-12.4 Ma, with most of the ashes probably being
10.2-11.5 Ma.
E
E
Coarse white ash zone (CWAZ) ― Numerous thin to medium, grayish white to white ashes containing fragments of consolidated ash
with minor pink to gray volcanic lithic grains (3-8%), quartz(?), and biotite grains (3-8%). Where they first appear in the stratigraphic
section, there are as many as ten of these ash beds recognized over a stratigraphic interval of 50-75 m (called the main coarse white ash
zone). The grain size is fine to very coarse ash. Locally it is altered to a greenish bentonite. Based upon data and observations, we use an
age range of 10.9-12.8 Ma for the CWAZ, with the majority of the tephra beds being 12.0-12.8 Ma (particularly the cluster of tephra beds
observed in the southern quadrangle, which lie below the Española tephra zone). The relatively few coarse white ash beds observed near
Black Mesa and north of the Rio Chama may be younger (12-10 Ma?).
Fine white ash east of San Juan Pueblo (FWAE) ― Greenish white, altered, fine ash. Lower 5-10 cm is hard, upper part is weakly
consolidated. Age unknown. 25-30 cm-thick. Interbedded within unit Tto.
Pojoaque black ash southeast of El Llano (PBA) ― Black ash, 0.1-1.0 mm in size, that is well sorted and locally mixed with sand of similar
size. The bed is up to 40 cm in thickness and located above the Pojoaque white ash zone. Correlates to black “basaltic lapilli” observed in
the Española quadrangle to the south, which are likewise located stratigraphically above most of the Pojoaque white ash zone (Koning,
2002a). Considering the age of the Pojoaque white ash zone (see below), this ash is probably 13.0-13.5 Ma.
Pojoaque white ash zone (PWAZ) ― Approximately six beds of thin to thick, tabular fine white ashes in a 95-100 m-thick stratigraphic
interval. Ash beds may be reworked and mixed with detrital sand, have a thickness of 10-100 cm, and are commonly internally planar- to
wavy-laminated. These ashes are generally altered and contain very sparse to sparse glass shards and up to 7% biotite. Gray ashes locally
preserved in the Pojoaque Member type section to the south (Galusha and Blick, 1971) are not observed in the study area. Chemical
comparisons from samples in the Española quadrangle suggest that most beds in the PWAZ came from the Southern Nevada volcanic
field (A. Sarna-Wojcicki, written commun., 2005). We interpret an age range of 14.0 to 13.2 Ma.
P
P
Subsurface Units Depicted Only On Cross Sections
Chama-El Rito Member of the Tesuque Formation (lower to middle Miocene) ― Pink to very pale brown, very fine to medium arkosic
sand with sparse volcaniclastic pebble-conglomerate channel-fills and mud beds.
Ttch
Lithosome B of the Pojoaque, Skull Ridge, and Nambe Members of the Tesuque Formation (lower to middle Miocene) ― Sandy
channel-fills interbedded with floodplain deposits composed of mudstone and fine-grained sandstone. Deposited by a river associated
with lithosome B. Lithologically similar to map units Ttbp2 and Ttbp1 but spanning older strata whose up-dip correlatives include the
Skull Ridge and Nambe Members of Galusha and Blick (1971).
Ttpbsn
Abiquiu and Picuris Formations, undivided (lower Miocene) ― Volcaniclastic sand, with some gravel and silt, derived from felsic to
intermediate volcanic centers to the north.
*u
Undivided Paleozoic strata (Mississippian to Permian) ― Limestone, siltstone, shale, and sandstone; under this quadrangle, most of this
unit is probably the Madera Limestone (Pennsylvanian). Thickness is uncertain.
Lower, mixed provenance unit of the Pojoaque member (middle Miocene) ― Very fine- to fine-grained sandstone, silty sandstone,
siltstone, and minor silt-rich mudstone. Color ranges from pink to light brown. Sand generally contains more potassium feldspar than
YXu
Undivided Proterozoic rocks (Mesoproterozoic to Paleoproterozoic) ― Granite, amphibolite, schist, gneiss, and quartzite as seen in
outcrops east of Chimayo at the foot of the Sangre de Cristo Mountains.
Qe
Ttmp2
Qtsc3
4
Ttbp1
4,000'
Qtsc4
Ttch
36°00'00"N
Tcc
Ttpbsn
Gradational geologic contact, location approximately
known.
Normal fault. Solid where exposed, dashed where
approximately known, dotted where concealed. Bar-ball
on downthrown side. Tic shows dip of the fault plane.
Right lateral strike-slip fault. Solid where exposed,
dashed where approximately known.
Right lateral oblique-slip fault. Solid where exposed,
dashed where approximately known. Bar-ball on downthrown side.
Left lateral oblique-slip fault. Solid where exposed,
dashed where approximately known, dotted where
concealed. Bar-ball on downthrown side.
Anticlinal fold. Dashed where approximately known.
Ttpbsn
Tap
Ttch
500m
Tap
*u
Tephras of the Tesuque Formation:
w
w
w
m
m
m
b
b
b
A
A
A
E
P
E
P
E
P
Ttch
Arroyo de los Peñita fine white ash (PFwa)
Arroyo de los Peñita fine black ash (PFba)
Chamita upper tuffaceous zone (CUTZ)
(dotted where concealed)
Upper coarse white ashes (CLTZw) Lower Chamita
tuffaceous
Middle mixed ash (CLTZm)
zone
Basal black ashes (CLTZb)
Basal Alcalde tuffaceous zone(?) under
Black Mesa (ATZb)
Fine, white pumice west of San Jose (FWPWSJ)
Española tephra zone (ETZ)
Coarse white ash zone (CWAZ)
(dotted where concealed)
Fine white ash east of San Juan Pueblo (FWAE)
Pojoaque black ash southeast of El Llano (PBA)
Pojoaque white ash zone (PWAZ)
0' MSL
Monoclinal fold. Dashed where approximately known,
dotted where concealed.
Tap
YXu
Tap
9
Strike and dip of inclined bedding.
Direction of downslope movement of landslide.
(t)
Paleocurrent vectors; tail of arrow is located at measurement. Measurements taken from: imbrication (i), channelaxis (c), foreset dip direction (f), tool marks, grooves (t).
Rak quarry
Fossil locality site.
SCV-1014051202-djk
Location of Ar-Ar sample and sample number.
Espanola #1
Domestic-water supply well.
Alcalde #1
Drill hole for hydrocarbon exploration.
106° 07' 30"
106° 00'
36°07'30"
Daniel Koning
36°00'
106° 07' 30"
YXu
*u
-1,000m
*u
36°00'
106° 00'
Mapping Responsibilities
Note: Depth estimates to basement rocks (*u and YXu)
were obtained using gravity data (provided by Sean Biehler).
YXu
-4,000'
YXu
-1,500m
-5,000'
B'
B
A geologic map displays information on the distribution, nature, orientation, and age
relationships of rock and deposits and the occurrence of structural features. Geologic and
fault contacts are irregular surfaces that form boundaries between different types or ages
of units. Data depicted on this geologic quadrangle map are based on reconnaissance field
geologic mapping, compilation of published and unpublished work, and photogeologic
interpretation. Locations of contacts are not surveyed, but are plotted by interpretation
of the position of a given contact onto a topographic base map; therefore, the accuracy of
contact locations depends on the scale of mapping and the interpretation of the geologist(s).
Any enlargement of this map could cause misunderstanding in the detail of mapping and
may result in erroneous interpretations. Site-specific conditions should be verified by
detailed surface mapping or subsurface exploration. Topographic and cultural changes
associated with recent development may not be shown.
The map has not been reviewed according to New Mexico Bureau of Geology and Mineral
Resources standards. Revision of the map is likely because of the on-going nature of
work in the region. The contents of the report and map should not be considered final
and complete until reviewed and published by the New Mexico Bureau of Geology and
Mineral Resources. The views and conclusions contained in this document are those of the
authors and should not be interpreted as necessarily representing the official policies, either
expressed or implied, of the State of New Mexico, or the U.S. Government. Cross-sections
are constructed based upon the interpretations of the authors made from geologic mapping,
and available geophysical (regional gravity and aeromagnetic surveys), and subsurface
(drillhole) data.
Kim Manley
*u
Tap
7,000
NW
feet ASL
6,000'
Cross-sections should be used as an aid to understanding the general geologic framework
of the map area, and not be the sole source of information for use in locating or designing
wells, buildings, roads, or other man-made structures.
Qtcg2a
Tcc
Tcc
Qay
Qtcg2a
5,000'
Qtcg2b
Qay
Tcvc
Qtcg2b
Tcv
Tto
Tto
Qtcg2c
Tcc
Tccu
Tcvc
Tcv
Española
#9 well
(projected)
Qay
Tcv
Española
#8 well
Tto
Tto
Ttpb2
SE
Rio
Grande
Ttpbsn
Española
#6 well
(projected)
Qay
Tto
4,000'
Ttpbsn
meters ASL
Ttpb1
1,500m
Ttch
Ttpbsn
Ttch
Ttpbsn
Ttch
Ttch
Ttch
2,000
Española
#4 well
Ttpb1
Ttpb2
Ttpb1
Ttch
Ttpbsn
Ttpbsn
1,000m
3,000'
C
36°07'30"
Erosional basalt knobs (see Koning, et al., 2005).
1
-500m
-2,000'
Comments to Map Users
Location of Rio Grande/Rio Chama basal terrace gravels,
Qrg
0m MSL
*u
Synclinal fold. Dashed where approximately known,
dotted where concealed.
(f)
1,000m
Ttch
Location of measured stratigraphic sections showing
stations.
(c)
1,500m
Ttmp1-2
Tto
2,000'
Ttmp1-2
Ttbp2
Tto
Tto
Tcv
Tto
Tcc
Tcc
Tcv
Tcc
2,000
meters ASL
Tccu
Tccu
Tcv
Tcc
106°00'00"W
Location of geologic cross section.
(i)
Tccu
Tcc
Ttbp1
Qtsc3
SE
Alcalde #1 well
(projected
along strike)
68
Tccu
Tcv
Qtsc3
409000
408000
Tcvc
Tcc
A'
Rio
Grande
Guique
Tgo
Tgo
Tcv
Qay
LC-a
Qtsc3
Tcv
Tsb
Tcc
Geologic contact. Solid where exposed or known, dashed
where approximately known, dotted where concealed,
queried where uncertain.
75
PUYE
Qtsc1
Tcc
Tcvc
6,000'
3985 000
Explanation of Map Symbols
VELARDE
1000
Qao Ttap1
LC-f
Qtsc1
P
403000
Ttbp1 Qay
Qtsc2
LC-g
Qtsc2
SCALE 1:24,000
MN
SAN JUAN
PUEBLO
P
P
05'00"
402000
3
Ttbp1
Tcv
Ttmp1
Ttmp1
4
P
Ttmp2
P
401000
Qtcg4
PP
P P
P
400000
Qrg
Qay
Base map from U.S. Geological Survey 1953, photorevised 1975, edited 1977.
1927 North American datum, Universal Transverse Mercator projection.
1000-meter grid, UTM zone 13, shown in blue.
LYDEN
P
Qe
Ttbp1
Qay
Chamita lower tuffaceous zone
Tccu
Tap
Cross section
C-C’
Santa Clara
Tsb over Tgo fault zone
?
PP
Qay
36°00'00"N
399000
P
Ttbp1
P
?
Qay
Qtcg3
3
Ttmp2
Qrg
106°07'30"W
Qay
Ttbp1
Qtcg2a
Tto
PP
P
Tto
Qay
P
5
NW
P
4
Qe
P
7,000
feet ASL
P
Qrg
P
Qtcg4
AM
Qtcg1
Qrg
P
P
Black
Mesa
A
5
Qao
LC-h
P
Qtcg2c
Qrg
Tto
TESUQUE FORMATION
GEOLOGIC CROSS SECTIONS
Ttmp2
LC-j
4
P LC-i
P
P
Qe
4
Sedimentary Rocks
CHAMITA FORMATION
?
Tsb
Lower lithosome A unit of the Pojoaque member (middle Miocene) ― Fine overbank and extra-channel sediment with ~5% coarse
channel-fill deposits. The former is silty very fine- to fine-grained, arkosic sandstone; color ranges from light brown to reddish yellow.
Minor beds of mudstone and siltstone occur. The channel-fill is composed of light yellowish brown, very fine- to very coarse-grained,
arkosic sandstone with local gravel near the base; gravel consists of pebbles of granite, 20% quartzite, and 5-10% reworked calcium
carbonate-cemented nodules. Deposit is weakly to moderately consolidated; about half of channel-fills are moderately to strongly
cemented by calcium carbonate. Found in a similar depositional environment as Ttap1 (i.e., distal alluvial slope). Unit overlies Ttbp1,
underlies Ttmp1, and appears to grade laterally westward into unit Ttmp1. 14.7-13.7 Ma old. ≤15 m thick.
70
Ttmp2
5
P
Tto
Tgo
3986 000
Qay
Espanola #4
Qrg
CHILI
Ttmp2
Ttmp2
Qtcg3
Qtcg2b
Tto
Qay
Ttmp2
P
?
Espanola #3
Ttmp1
?
Tgy
Ttbp2
Ttbp2
Ttbp2
4
Espanola #2
MEDANALES
P
3
Qtcg2a
LC-I
79
4
5
Qay
3985000
Ttap2
5
Tto
8
1
LC-m
Ttap2
Tto
Qtc2
LC-n
1
LC-I'
Ttbp2
LC-k
3
Espanola #8
Tto
Qtcg2a
5
Espanola #9
East Llano
4
Ttap1
Middle terrace deposit of Rio Chama-Rio Grande confluence near Chamita (upper to middle(?) Pleistocene) ― 4-6 m of quartzite-rich,
axial river sandy gravel overlain by 1-20 m of interbedded floodplain and tributary piedmont deposits. The basal sandy gravel consists
of fine- to very coarse-grained sand, cobbles, pebbles, and 1-5% boulders. Floodplain deposits consist of interbedded light yellowish
brown very fine- to fine-grained silty sand with minor (~5%) thin beds of fine- to very coarse-grained sand and pebbly sand derived from
local tributary drainages. Tributary piedmont deposits consist of silty very fine- to medium-grained sand and pebbly medium- to very
coarse-grained sand; pebbles have a composition reflecting the provenance of the drainage. Strath is 30-45 m above the Rio Grande. Unit
correlates to Qtr2, Qtcg3, and possibly Qtcg2c. 70-150 ka old. Loose. 4-26 m thick.
Ttap2
Qay
Qtcg3
Qrg
5
?
?
Qrg
af
Qrg
Qay
Qtcg2a
Qtcg1
Tto
3987 000
Ttbc
3
Ttbc
Qrg
Qtcg2b
TtoSCV-1014051202-djk
LC-r
LC-o
Qtc3
?
Chamita lower tuffaceous zone (CLTZb, CLTZm, CLTZw) ― The Chamita lower tuffaceous zone occupies the interval about 85-115
m (280-375 feet) above the base of the Chamita type section (Galusha and Blick, 1971). Wthin this ~ 30 m interval are three distinctive
subintervals. The lowest, CLTZb, consists of two thick beds (80-110 cm each) of grayish coarse ash and lapilli separated by 2.8 m of
siltstone and fine sandstone. Vesicularity of some lapilli clasts suggest a basaltic composition, but an intermediate to felsic composition
is also possible. Approximately 9-15 m above the lower subinterval is the middle subinterval, CLTZm, which is composed of two beds
spaced 3 m apart. The lower bed consists of altered, pebble-size clasts of consolidated white ash; the upper bed is composed of a 40
cm-thick bed of silt mixed with poorly sorted, angular basaltic pebbles and pebble-size consolidated white ash. The upper, whitish
subinterval, CLTZw, lies 9-15 m above the middle. It is composed of a ledge-forming, 50-55 cm-thick, white bed of pumiceous coarse ash
with ~ 20% black biotite and hornblende(?). 40Ar/39Ar dating of a tephra (probably the upper subinterval) and revision of the Chamita
Formation magnetostratigraphy of MacFaden (1977) by McIntosh and Quade (1995) indicates an age range of 7.7-8.4 Ma for this zone.
w
w
Upper, mixed provenance unit of the Pojoaque member (middle Miocene) ― This extensive unit is comprised of overbank and extrachannel sandstone and siltstone, with minor channel-fills of sandstone and pebbly sandstone of either lithosome A, lithosome B, or a
mix between the two. The former two are comprised of light brown to pink siltstone and very fine- to fine-grained sandstone, with
minor mudstone (the sand has varying proportions of pinkish potassium feldspar from northeast-derived lithic grains). Channel-fills
are composed of very pale brown to pale brown, very fine- to very coarse-grained sandstone and sparse pebbles derived from either
lithosome A, lithosome B, or mixed provenances. Over most of the map area, this unit represents deposition near the transition between
the basin floor (lithosome B) and distal portions of the alluvial slope (lithosome A). It overlies Ttmp1 and underlies Ttbp2. Interpreted
age of 13.2-14.0 Ma. 70-75 m thick.
Ttmp2
Lower terrace deposit of Rio Chama-Rio Grande confluence near Chamita (upper Pleistocene) ― 2.5-4 m of quartzite-rich, clastsupported, axial river sandy gravel overlain by floodplain and/or tributary piedmont deposits. The sand is pale brown to light yellowish
brown and medium- to very coarse-grained; gravels are subrounded to rounded pebbles and cobbles (with 5-10% boulders) and dominated
by quartzite with lesser volcanic rocks. Floodplain sediment is light yellowish brown siltstone and very fine-grained sandstone. Adjacent
to Black Mesa and west of El Duende, the terrace deposit is thicker (as much as 38 m). Strath is approximately 6-12 m above the Rio
Chama. Unit correlates with Qtcg4. 12-45 ka old. Loose. 6-40 m thick.
LC-p
Middle Llano Ttap2
2
Qay
AM
?
Qay
LC-q
Ttap2
Ttap2
Tto
Tcc
Love
fossil site
5
Qtcg4
Qrg
Tto
West Llano
3
Qtcg3
Qtcg2a
Tcc
Ttbc
Ttbp2
2
Qay
Ttbc
Qrg
Qtcg2b
Qtcg1
Ttbc
2
Tto
Qrg
Qrg
Tto
3
Ttbc
Qay
Qtcg4
Qtcg2b
Tto
Ttap2
Qtsc1
?
Chamita upper tuffaceous zone (CUTZ) ― Yellowish white to white pumice (lapilli or coarse ash in size), mixed with various proportions
of detrital sand. Commonly found in thick, well consolidated ledge-forming beds. Pumice is found in at least five relatively continuous
beds, but several other non-continuous pumice beds are present. South of Arroyo de los Borregos, these bed(s) are hard, poorly sorted,
slightly muddy, brownish, pumiceous phreatomagmatic(?) deposits in medium to thick, tabular beds. The age of pumice is relatively
well-constrained at 6.8-6.9 Ma, and correlative to the Peralta Tuff (McIntosh and Quade, 1995).
Upper lithosome B unit of the Pojoaque member (middle Miocene) ― Generally floodplain deposits with minor channel-fill deposits
of sandstone to pebble-conglomerate. Floodplain deposits are mostly light brown to brown mudstone, claystone, and siltstone, with
subordinate very fine- to fine-grained sandstone to silty sandstone. Channel-fill sandstone is pale brown, very fine- to very coarse-grained,
and contains an approximate ratio of 50-80% northeast-derived lithic grains to 20-50% pinkish potassium feldspar grains. The pebbleconglomerate locally include up to 40% cobbles; gravel composition is dominated by Paleozoic limestone, sandstone, and siltstone, with
10-20% quartzite, 5-15% quartz and chert, 1-10% granite, and 1-30% intermediate to felsic volcanic clasts. The unit represents a major
south-southwest-flowing river system. It overlies Ttmp2 on this quadrangle. 13.2-13.6 Ma old. ~30 m thick.
Ttbp2
Terraces deposited near the confluence of the Rio Chama and Rio Grande near Chamita
LC-t
LC-s
Ttbc
Qrg
Tcv
Qrg
Volcanic/
Volcaniclastic
Rocks
Arroyo de los Peñita fine black ash (PFba) ― Black, fining-upward bed of lapilli (near base, up to 7 mm-long) to fine ash; well consolidated,
relatively pure, and 10 cm-thick. Age unknown.
Upper lithosome A unit of the Pojoaque member, informal salmon-colored unit (middle Miocene) ― Overbank and extra-channel
sediment with 3-15% coarse channel-fills. The former two are generally light brown to reddish yellow, very fine- to fine-grained arkosic
sandstone and silty sandstone, with minor siltstone and mudstone. Channel-fills are composed of sandstone, pebbly sandstone, and
pebble-conglomerate; sand is arkosic, very fine- to very coarse-grained, and conglomerate clasts are granitic with 1-5% quartzite, and
include minor cobbles. Deposits are well to moderately consolidated and represent deposition on the distalmost alluvial slope associated
with lithosome A. Its informal color desiginant is from Galusha and Blick (1971), due to the common reddish to pinkish hue of its strata.
Unit pinches out westward within unit Ttbp2, and is underlain by the same. 13.0 -13.3 Ma old. 30-40 m thick.
Ttap2
Quartzite-rich, basal sandy gravel mapped in terraces near the confluence of the Rio Grande and Rio Chama (middle to late Pleistocene)
― Axial sandy gravel found at the base of several terraces near the confluence of the Rio Grande and Rio Chama. The sand is pale brown
to light brownish gray to gray, fine- to very coarse-grained, subrounded to subangular, poorly to well sorted, and rich in lithic grains.
Gravel is clast-supported, subrounded to rounded, poorly sorted, and consists of pebbles, cobbles, and up to 5% boulders. Loose. 2-5 m
thick.
71
2
4
Ttbc
Tto
9
Qay
Qtcg3
Tto
Tto
75
LC-u
5
3
Qtcg3
Qrg
Tcc
2
Tto
Tcv
Qay 6
6
Qtcg3
Tcv
Tcv
7
Tto
Tcv
7
Qtcg2c
Tcc
?
3987000
Qrg
Qay
Tcc
Tcv
Tto
8
Qtcg4
?
?
Qtcg2c
3988 000
Ttac
Ttbc
AM
SCV-946fu251102-djk
Tcv
5
AM
Qtcg1
Qtcg1
E
Qrg
6
Qtcg2c
SCV-948-251102-djk
Qtcg3
5
Tcc
Qtcg3
LC-v
Qay
Qtcg3
Tcv
4
Qay
?
Tephras Of Tesuque Formation
Ojo Caliente Sandstone member (middle Miocene) ― Very fine- to medium-grained, largely cross-stratified sandstone deposited in
a large, dune field, whose colors range from very pale brown to white; contains minor beds of siltstone, mudstone, and claystone. This
unit interfingers eastward with unit Ttbc, and probably interfingers with units Ttbp2 and Ttmp2 in the subsurface near Española; it is
overlain by Tcv in the western part of the quadrangle. ~11 to 13.5 Ma old. Cross sections and well control indicate 220-350 m of thickness,
but possibly as thick as 440 m near the northern boundary of the quadrangle.
Tto
Upper terrace deposit of Rio Chama-Rio Grande confluence, overlain by volcaniclastic alluvium from local tributary drainages
(middle Pleistocene) ― 2-3 m of quartzite-rich, axial river sandy gravel (see Qrg description below) overlain by floodplain deposits,
which in turn are overlain by volcaniclastic alluvium from western tributary streams. Channel-fill sand is gray to pale brown. Floodplain
deposits are very pale brown silt to mud, with minor sand and ~3% pebbles (mostly volcanic); up to 4 m thick where observed. Western
tributary volcaniclastic alluvium is sandy gravel to gravelly sand, with pale brown, very fine- to fine-grained sand, locally silty, and
channel-fill gravel of volcanic pebbles, subordinate cobbles, and sparse (up to 10%) boulders, which become more common up-section.
Strath is 90-126 m above the Rio Grande and Rio Chama. Lower parts of deposit locally have the Lava Creek B ash to the west (Dethier
et al., 1990). Age ranges from350 to 650 ka. Loose to weakly consolidated. 4-20 m thick.
Qtcg1
SCV-318230702-djk
2
Ttbc
Tcc
LC-AA
5
Qao
af
Qrg
?
Tch
Qrg
E
LC-z
E
Tcc
LC-BB
4
2
2
Qay
10
02'30"
Qay
?
Tccu
Qay
Ttbc
Qao
74
2
Tto
San Juan Pueblo
casino
Qtcg2a
3989 000
Ttac
Ttbc
Tcvc
AM
Qay
Qao
Qao
13
Tcc
Qtcg2b
Tto
?
Arroyo de los Peñita fine white ash (PFwa) ― White, fine ash rich in glass shards and with only trace mafic minerals; 10 cm-thick.
Possibly the youngest ash currently known in the basin-fill sediment. Age unknown.
Coarse upper lithosome B unit, Cejita member of Tesuque Formation (middle to upper Miocene) ― Floodplain deposits with varying
proportions of coarse channel-fill deposits of sandstone and conglomerate. The former consists of light brown to pink very fine- to finegrained sandstone and silty sandstone, occasionally containing beds of light brown to brown mudstone and claystone. Channel-fill
sandstones are pale brown to very pale brown, fine- to very coarse-grained, and generally has an estimated ratio of 50-80% northeastderived lithics to 20-50% pink potassium feldspar. Channel-fill conglomerate consists of pebbles with minor cobbles; clast composition is
dominated by Paleozoic limestone, sandstone, and siltstone, with minor quartz, felsic to intermediate volcanic rocks, and granite. Clast
composition becomes progressively more granitic to the east so that granite is about subequal. Ttbc represents a large river drainage
that flowed south-southwest from the Peñasco Embayment, and had a source in the Sangre de Cristo Mountains north of Truchas Peaks.
The Cejita Member interfingers eastwards with unit Ttac, and westwards with unit Tto. Age is inferred at 9-13 Ma, thickness is 65-75 cm.
Ttbc
Middle terrace deposit of Rio Chama-Rio Grande confluence, overlain by volcaniclastic alluvium from local tributary drainages
(middle to upper Pleistocene) ― 3-5 m of quartzite-rich, axial river sandy gravel (see Qrg description below) overlain by younger
volcaniclastic brownish gray to light yellowish brown sand and gravel derived from western tributary streams; both are locally
interbedded with floodplain deposits. Qtcg2 can be subdivided into three subunits (a-c = oldest to youngest) based on different respective
gross elevations and ages of the basal sandy gravel (see Figure 1). The overlying volcaniclastic alluvium, however, covers all three levels
and appears to have been emplaced following the deposition of the lowest level of axial river gravel, but prior to the next incisional
episode associated with Qtcg3. Floodplain deposits are composed of silt and silty very fine- to fine-grained sand. Unit correlates to Qtc1
and Qtr1. The strath heights of terraces deposits Qtcg2c, Qtcg2b, and Qtcg2a are approximately 35-47 m, 50-64 m, and 67-84 m above the
modern Rio Grande, respectively. Qtcg2c and Qtcg2b have estimated ages of 130-150 ka while Qtcg2a is believed to be 250-280 ka old
(based upon Dethier and Reneau, 1995; Table 3). Loose to weakly consolidated. 15-23 m thick.
Qtcg2c
81
Qtcg2b
3988000
Ttac
Ttbc
1
Tto
Qay
Tcc
Qrg
3990 000
Ttbc
Ttbc
67
Qao
9
6
Qao
Ttbc
Qtsc2
Qlsi
Lower lithosome B unit of the Pojoaque member (middle Miocene) ― River and stream floodplain deposits with 10-30% channel-fill
deposits. Floodplain sediment consists of brown to reddish brown mudstone to claystone together with pale brown to light yellowish
brown siltstone and very fine- to fine-grained sandstone, weakly to moderately consolidated. Channel-fill deposits consist of sandstone,
pebbly sandstone, and sandy pebble-conglomerate with minor (<10%) cobbles that locally fines-upward. Channel-fill sand is commonly
medium- to very coarse-grained and has an estimated ratio of 50-70% northeast-derived lithics to 30-50% pinkish potassium feldspar
grains; gravel clasts consist of Paleozoic sandstone, siltstone, and limestone with roughly 15-25% intermediate to felsic volcanic rocks,
5-10% quartzite, 1-3% vein quartz, and 0-1% granite. Interpreted depositional environment is one of a relatively gentle basin floor
with scattered broad and meandering channels draining highlands located east of the Peñasco embayment. It underlies Ttmp1 on this
quadrangle. 13.5-14.9 Ma old. 115-125 m thick.
Ttbp1
Coarse, upper lithosome A unit (middle to upper Miocene) ― Extra-channel and overbank sediment with 10-30% coarse channel-fill
complexes. The former consists of light brown to reddish yellow, very fine- to medium-grained arkosic sandstone and silty sandstone,
with minor siltstone and mudstone. Channel-fill complexes consist of arkosic pebbly sandstone and sandy pebble-conglomerate with
minor cobbles. This unit both overlies and interfingers westward with unit Ttbc (which west of the Rio Grande is called Tcc); its lower
contact is gradational with Ttbc over 6-9 m. Age is inferred at 9-12.8 Ma. Approximately 100-180 m thick in the east-southeast part of the
quadrangle.
Ttac
Lower terrace deposit of Rio Chama-Rio Grande confluence, overlain by volcaniclastic alluvium from local tributary drainages (upper
Pleistocene) ― 3-4 m of quartzite-rich, axial river sandy gravel (see Qrg description below) overlain by younger volcaniclastic brownish
gray to pale brown sandy gravel and gravelly sand derived from western tributary streams; both are locally interbedded with floodplain
deposits. The overlying volcaniclastic sediment consists of light brownish gray to pale brown, fine- to very coarse-grained sand, gravelly
sand, and sandy gravel comprised of volcanic pebbles, cobbles, and boulders in varying proportions. The floodplain sediment consists
of pale brown to reddish yellow silt and very fine-grained to medium-grained sand and silty sand, with minor coarser sand and 1-5%
pebbles. Terrace strath is approximately 27-38 m above the Rio Grande. Unit correlates to Qtc2 and possibly Qtr2. 70-90 ka old. Loose to
moderately consolidated. 7-20 m thick.
Qtcg3
Ttbc
?
Qtcg2a Qtcg2b
Tcc
Qtcg2a 5
B
Qay
Tcc
AM
3990000
5
Qrg
A'
Ttbc
10
C
Ttbc
Ttbc
Qtr2
Qtc1
Qtcg1
Qls
northeast-derived lithic grains. Unit is well consolidated and a distinctive ledge-former. Some or many beds may have been deposited as
eolian sand sheets in the overall transition depositional setting between lithosome B basin floor and lithosome A alluvial slope. It overlies
Ttbp1 and underlies Ttmp2. 13.7-14.7 Ma old. 30-35 m thick.
Tesuque Formation
Lowermost terrace deposit of Rio Chama-Rio Grande confluence (upper Pleistocene) ― Light yellowish brown to very pale brown,
subrounded to rounded, sandy gravel. The sand is fine- to very coarse-grained and the gravel is comprised of subequal pebbles and
cobbles, with 1-2% boulders, dominated by quartzite, granite, and quartz. Strath is 5-12 m above the Rio Grande. Unit correlates with
Qtc3. 12-45 ka old (based upon Dethier and Reneau, 1995; Table 3). Loose. ~5-6 m thick.
Qtcg4
Qay
5
Qtr2
12
13
12
Grande and Rio Chama. These terraces generally consist of a 2-5 m-thick, quartzite-rich, axial river gravel (subscript “a” on the unit labels; designated as
marker bed Qrg, where exposed) overlain by volcanic sediment derived from the west (subscript “v”). The UTM NAD 27 zone 13 southeast and northwest
coordinates are respectively: 3984000 N 402980 E; 3986190 N 398630 E. Figure corresponds to Figure 5 in the accompanying report.
Tcc
Qtr1
Qao
Qtsc3
2500
Interbedded Vallito and Cejita Members (upper Miocene) ― Interbedded intervals commonly several meters thick are located in
the west-central San Juan Pueblo (Ohkay Owingeh) reservation. It contains a bed of the CWAZ, but lies well below the Chamita lower
tuffaceous zone (CLTZ); estimated age is 10-13 Ma. Total thickness of approximately 170-250 m.
Tcvc
Figure 1. Northwest-trending cross section showing inset relations of western Quaternary terrace deposits deposited near the confluence of the Rio
3991 000
5
3
Qrg
Qay
Tto
AM
3991000
Ttac
4
Qtcg2a
?
PROTEROZOIC
Vallito member (upper Miocene) ― Pink to very pale brown, very fine- to medium-grained sandstone and silty sandstone interbedded
with <30% light yellowish brown to very pale brown siltstone and claystone. Moderately to well consolidated. Unit is interpreted to
primarily reflect low-energy river deposition on a flat basin floor, where most of the sandy strata were probably deposited in broad
channels of a river braidplain(?). Minor eolian deposits of sand sheets and sand dunes were also present. Unit lies stratigraphically below
the coarse white ash zone (CWAZ), and extends into the lowest part of the Chamita type section, giving it an age range of 9-13 Ma.
Tcv
2
Qtr2
AM
Tcv
Tcc
Qay
Qay
Ttac
Qao
318
542
Hernandez member (upper Miocene) ― Light yellowish brown to pale brown floodplain deposits of siltstone, very fine-grained
sandstone, and mudstone, interbedded with about 10% medium to thick channel-fills of pebbly sandstone to sandy pebble-conglomerate.
Channel-fill sand is light gray to light brownish gray and fine- to very coarse-grained; subrounded pebbles primarily consist of felsic
to intermediate volcanic clasts. 10-20% of channel-fills are strongly to moderately cemented by calcium carbonate. The unit represents
deposition from river systems derived from the north-northwest, appearing to interfinger with the western Cejita member. ~8-10 Ma old.
Up to 16 m thick.
Tch
3992 000
Qtc2
Tcc
299
Cejita Member (upper middle to upper Miocene) ― Light brown to light yellowish brown to very pale brown floodplain deposits of
siltstone-claystone and fine sandstone that are interbedded with various proportions of coarser channel-fill deposits of sand and pebbledominated conglomerate. On the western slopes of Black Mesa within the fine-grained sediment, the coarser channel-fill deposits make
up about 10% of the deposit, and the channel-fill gravels consists of pebbles and fine cobbles, dominated by 35-60% quartzite and 15-45%
green-gray Paleozoic limestone, sandstone, and siltstone. On the southern tip of Black Mesa, this unit fines-upward, and is composed
of interbedded floodplain and channel-fill deposits of sandstone, pebbly sandstone, and sandy pebble-conglomerate. There are minor
intervals of deposits correlative to the Vallito member (Tcv), and locally much of the sand looks to be reworked from Ojo Caliente
Sandstone (Tto). 5.8 to 12.8 Ma old. 150-200 m thick.
Tcc
4
Qay
Qtcg2
Qtsc4
Qtc2
16.4
Coarse, upper lithosome A unit, tuffaceous (upper Miocene) ― Coarse, upper lithosome A unit, as described above, mixed with pumiceous
ash and interbedded with the Chamita upper tuffaceous zone (CUTZ). Individual CUTZ beds are not differentiated here because of their
abundance and because of extensive mixing of ash with detrital sediment. Estimated maximum thickness of approximately 40 m.
Tccut
Ttac
Qao
Qay
15.0
Coarse, upper lithosome A unit (upper Miocene) ― Light brown to reddish yellow to pink, silty sandstone and sandy siltstone
with subordinate channel-fill complexes of arkosic pebbly sandstone and sandy conglomerate. Sand is mostly very fine- to mediumgrained outside of the coarser channel-fill complexes; gravel consists of subrounded to subangular pebbles with minor local cobbles
and are composed of granite with about 15-40% quartzite. West-northwest paleocurrent flow data together with the granite-dominated
composition of the gravel support derivation from the Sangre de Cristo Mountains south of the Peñasco embayment. South of the Rio
Chama, this unit is composed of light brown to pink siltstone and very fine to fine-grained sandstone, silty sandstone, and sandy siltstone.
Pebbles are generally granitic. Here, this unit was deposited on the distal alluvial slope in a relatively low-energy environment. 5.8 to 12.0
Ma old. The unit attains a maximum thickness of 200-250 m east of the south tip of Black Mesa.
Tccu
The terrace deposits located to the west and northwest of Española generally consist of a 2-5 m-thick, quartzite-rich, basal gravel (including
the prominent marker bed, Qrg, described below) deposited by the axial drainages (i.e., the Rio Grande and/or the Rio Chama), overlain
by volcaniclastic piedmont alluvium, deposited by western tributaries to these rivers (see Figure 1 below). We did not attempt to
differentiate Rio Grande versus Rio Chama deposits in this area.
10
11.2
See the accompanying report for a discussion on the Chamita Formation, complete with measured stratigraphic type section.
Western Terraces deposited near the confluence of the Rio Grande and Rio Chama
9
Ttac
4
3993 000
Qay
Ttac
AM
Ttbc
Qrg
Ttac
Ttac
Qay
Qay
8
Qtc2
Qao
10.0
Chamita Formation
Uppermost terrace deposit of Santa Cruz River (lower Pleistocene) ― Composed of sandy gravel, with locally minor silt. Sand is light
yellowish brown and very fine- to very coarse-grained, and gravels are subrounded, although granitic clasts may be subangular. Strath is
96-102 m above the Santa Cruz River. This unit may correlate with Qtcg1. Interpreted age range of 350-650 ka. 2-8 m thick.
Qtsc1
Qao
Ttbc
7
Ttac
5
12
Ttbc
Qtr2
10
10
Qrg
Chamita
municipal
3992000
12
6
7
Ttac
Qao
10
Qtc2
Qay
05'00"
Ttac
Qay
Ttac
73
7
5
5.3
Miocene Basin Fill
Upper terrace deposit of Santa Cruz River (lower to middle Pleistocene) ― Light yellowish brown sandy gravel. Sand is very fine
to very coarse and the subequal cobbles and pebbles are rounded to subrounded, except some subangular granitic pebbles. Strath is
approximately 88-90 m above the Santa Cruz River. This unit may correlate with either Qtcg1 or Qtcg2a. Interpreted age range of 250500 ka. Loose. 1-6 m thick.
Qtsc2
3.6
Lower, older gravel underlying Servilleta Basalt flows (lower Pliocene) ― Sandy gravel, sand, and silty sand. Sand is pale brown to
very pale brown and very fine- to very coarse-grained. The silty sand may reflect floodplain deposition. Gravel is rounded to subrounded
pebbles and cobbles with local minor (5-10%) boulders, and predominantly quartzite with minor granite. Paleoflow data and sediment
characteristics suggest two differing source rivers: the western margin of Black Mesa contains 1-5 m of loose to weakly consolidated
sediment, deposited possibly by the ancestral Rio Ojo Caliente, flowing towards the south to southeast; in eastern exposures, the gravel is
overlain by up to 9 m of light brown to reddish yellow sediment very similar to unit Tccu, for a total thickness of 6-17 m, representing an
axial river system interpreted to be derived from the Sangre de Cristo Mountains near the Peñasco embayment and the southern San Luis
basin and may be the ancestral Rio Grande. This river may possibly have merged with an ancestral equivalent of the Rio Ojo Caliente
near the southern tip of Black Mesa.
Tgo
Middle terrace deposit of Santa Cruz River (middle Pleistocene) ― Light yellowish brown to light brown sandy gravel (color from sand)
inset into the Tesuque Formation north of the Santa Cruz River. Gravel is mostly subrounded and consists of cobbles with subordinate
pebbles. Sand is very fine- to very coarse-grained. Locally overlain by Qe up to 2 m-thick. Strath is 67-75 m above the Santa Cruz River.
This unit may correlate with Qtcg2a, Qtc1, and Qtr1. Interpreted age range of 250-280 ka. 1-4 m thick.
Qtsc3
5
Tccu
Tcc
Qtc3
Qrg
3994 000
Ttac
5
10
Tcc
5
3
Tcc
3993000
Qtr2
Qtc3
15
Qrg
Qay
Qao
Ttac
3
3
7
52
Qay
5
2
5
10
1
4
2
4
Tccu
10
85
3
Ttac
Tcc
Tcc
Tcv
05'00"
QTse
Qao
5
Qao
Qe
Qtr2
1.806
Servilleta Basalt flows (Pliocene) ― Dark gray, vesicular basalt forming an erosionally resistant, protective cap on top of Black Mesa.
Vesicules are commonly in discrete zones. Unit has been deformed by Plio-Pleistocene tectonic activity along faults under and adjacent
to Black Mesa. On the western margin, there is generally one flow 3-8 m thick; flows are commonly more numerous along the eastern
margin. A sample of the basalt from this quadrangle (UTM NAD 27 zone 13 coordinates: 3996100 N, 400970 E) yielded an 40Ar/39Ar age
of 3.32 ± 0.78 Ma.
Tsb
Lower thick terrace deposit of Santa Cruz River (middle to upper Pleistocene) ― There are two types of sediment in this deposit: a
light yellowish brown to light brown (7.5-10YR 6/4) finer sand and mud largely associated with a river floodplain, and a coarser sand
and gravel associated with a large axial river channel-fill, often preserved near the top. Together, these form a thick, relatively extensive
terrace deposit that is inset into the Tesuque Formation north of the Santa Cruz River. In the coarse channel fill, sand is medium- to very
coarse-grained, and the gravel consists of rounded to subrounded cobbles and pebbles. Floodplain deposits consist of silty very fine- to
fine-grained sand and mud with 10% coarse to very coarse sand and pebbles, weakly consolidated to loose. Strath is 27-34 m above the
Santa Cruz River and 60 m above the Rio Grande. All terrace ages are based upon correlation interpretations to Rio Grande terraces dated
by 14C and amino-acid racemization dating (Dethier and McCoy, 1993; Dethier and Reneau (1995); the age range of Qtcg4 is either 70-90
ka or 120-150 ka. 1-15 m-thick.
Ttac
18
Qay
Qay
8
Ttbc
Qtc3
Qtcg4
Qtcg3
QTse
Younger, upper gravel overlying Servilleta Basalt flows (lower to upper Pliocene) ― Thin (≤1 m) gravel overlain by silt and fine sand;
latter is similar to QTse in physical characteristics and possibly in age. The gravel is composed of pebbles and cobbles of basalt, with
1-15% very fine to very coarse pebbles similar in composition to unit Tgo. Both gravel and finer, overlying sediment is estimated to be
0.5-4.0 m thick.
Tgy
Santa Cruz River Terraces
3995 000
Qtsc4
Qay
?
5
Qao
Qao
Alcalde #1
87
Tccu
Qao
76
Ttac
Qtr1
4
?
2
5
9
Ttbc
?
Tgo
5
5
13 58
Qlsi
4
Landslides
Pliocene basalt flows and subjacent river deposits
Individual landslide (middle to late Pleistocene) ― This unit denotes a specific landslide complex at the center of the northern
quadrangle boundary. It consists of Chamita Formation (Tcc and Tccu) and talus and blocks of Servilleta Basalt (Tsb), which have
slowly slumped downward and eastward since major incision of the Rio Grande after ~3.5 Ma. The landslide complex is marked by
contorted bedding, small-scale faulting, and an overall bulbous or lobate geomorphic shape. Basal slide planes are not exposed. Weakly
to moderately consolidated. The toe of the landslide directly abuts the Rio Grande. Erosion of the toe of the landslide by the river may
create destabilization and further movement. Thickness unknown.
Ttac
4
5
4
5
Qay
Ttbc
3
5
Tsb
Ttbc
4
8
3
Tgo
4
Qay
Tccu
3 5
2
Qtr2
Qtr2
Sync 2
line
Tgo
QTse
5
11
Tcc
4
Tgo
6
ita
Cham
Tgo
Tcvc
4
24
Rak quarry
Qls
Tcv
13
3
8
?
?
Ttbc
12 San Juan quarry
1.0
Tertiary
Landslide deposits, undifferentiated (middle to upper Pleistocene) ― Large masses of Chamita Formation (primarily Tcc), together
with talus and large blocks of Servilleta Basalt (Tsb), which have slumped and slid eastward since major incision of the Rio Grande
after ~3.5 Ma. Basal slide planes not exposed. Landslides marked by contorted bedding, small-scale faulting, and bulbous or lobate
geomorphic shapes. Weakly consolidated. Thickness unknown.
Qls
Qao
Qay
22
27
Tgo
Tcvc
Qtr2
Tcc
Tgy
Tsb
Ttbc
3996 000
?
3996000
Ttac
Qay
Tgy
0.781
Slopewash and eolian deposits overlying down-dropped basalt flow blocks (upper Pliocene to Pleistocene) ― Very pale brown to
light yellowish brown silt and very fine sand, with subordinate fine to coarse sand, interpreted to be wind-blown fines locally reworked
by slopewash processes that mixed in detritus from the Chamita Formation and Servilleta Basalt. ~3% of beds are strongly cemented by
calcium carbonate. Loose to weakly consolidated.
QTse
late
0.126
Plio-Pleistocene volcanic and sedimentary rocks
Older alluvium (middle to upper Pleistocene) ― Tan to brown pebbly sand, sand, and sandy pebbles. Sand is very fine- to very coarsegrained and arkosic. Pebbles are generally granitic with minor quartzite; gravel may include 10-30% cobbles. Unit was deposited after the
terrace units Qtr1 and Qtc1 were abandoned. East of the Rio Grande, unit Qtr2 is both locally cut on top of or laterally grades into this
unit, and thus is similar in age. Interpreted age range of 50-300 ka. Loose to weakly consolidated, and 1-12 m thick.
Qao
Ttac
0.012
Upper terrace deposit of Rio Grande above confluence with the Rio Chama (middle Pleistocene) ― Sandy gravel to gravelly sand;
gravel consists of subequal pebbles and cobbles dominated by quartzite and basalt. Strath is 82-86 m above the modern Rio Grande. Unit
correlates to Qtcg2a and possibly Qtc1. 250-350 ka old. Loose and 3-4 m thick.
Qtr1
Younger alluvium (Holocene) ― Yellowish brown (10YR 6/4) to very pale brown (10YR 7/3) sand, silt and clay, silty sand, gravelly sand,
and sandy gravel that underlie modern valley floors. Sand is very fine- to very coarse-grained; gravel consists of pebbles and cobbles.
Basal contact not generally exposed, but drilling and seismic data indicate a maximum thickness of 32 m near east of Española, overlying
older (Pleistocene?) sandy gravels deposited by the ancestral Rio Grande (Johnpeer et al., 1985). Near El Llano, samples from this unit
were <3,000 14C yr BP (Johnpeer et al., 1985).
Qay
Ttbc
Qtr2
Tgo
Ttac
6
3997 000
Lower terrace deposit of Rio Grande above confluence with the Rio Chama (upper to middle Pleistocene) ― Sandy gravel consisting of
pebbles with 25-40% cobbles. Unit includes interbeds of unit Qao and laterally grades into Qao. Strath is 35-49 m above the modern Rio
Grande. Unit correlates to Qtc2, Qtcg2c, and possibly Qtcg3. Terrace deposit is 70-150 ka (probably 130-150 ka) old (based upon Dethier
and Reneau, 1995). Loose. Up to 12 m thick.
Qtr2
Rancholabrean
Qay
Qay
Qtr2
83
Older eolian sand deposits of the Española Formation (middle to upper Pleistocene) ― Yellowish brown (10YR 6/4) to very pale brown
(10YR 7/3) silt, very fine- to fine-grained sand and sandy silt, with minor coarser sand and pebbles. Deposit is generally massive and
overlies gravelly Santa Cruz River terrace deposits or high-level erosion surfaces east of Española. Pebbles and coarser sand, laid down
by streams, are generally located near the lower contact; wind-blown sand and silt were then deposited on top of this coarse, relatively
thin sediment. Cumulic soil development is inferred, and soils locally contain Bt horizon(s) (many faint to distinct films on ped faces)
overlying calcic horizons with stage II carbonate morphology. Interpreted age range of 10-300 ka (Galusha and Blick, 1971; Dethier and
Reneau, 1995). Loose to weakly consolidated and 1-3 m thick.
Qe
Irvingtonian
Tcc
Blancan
Ttbc
Rio Grande terrace deposits above the confluence of the Rio Chama
Artificial fill (recent) ― Compacted sand, silt, and gravel used for highway fill.
af
Ttbc
Terrace Alluvium
Qay
Hemphillian
7
71
Eolian
Clarendonian
50
7
Quaternary
86
14
Alluvium
0
Barstovian
Tsb
Qtr2
CORRELATION OF MAP UNITS
middle
7 Tcc
Upper terrace deposit of Rio Chama-Rio Grande confluence near Chamita (middle Pleistocene) ― 4-6 m of quartzite-rich, axial river
sandy gravel interbedded with subordinate (10-20%) floodplain deposits. Quartzite-rich gravel consists of subequal cobbles and pebbles,
with boulders present near base of deposit. Floodplain deposits are light yellowish brown siltstone and very fine- to fine-grained
sandstone. Strath is 71-75 m above the Rio Grande. Unit correlates to unit Qtgc2a and possibly Qtr1. 250-280 ka old. Loose. Up to 12 m
thick.
Qtc1
(Partial description of units;
complete descriptions, including ashes and references, are found in the accompanying report.)
Qlsi
Tcc
Qls
7
Qay
36°07'30"N
3998 000
early
Qay
Description of Map Units
106°00'00"W
409000
408000
late
5
Tto
407000
15
Tcvc
3998000
02'30"
406000
early
405000
late
C'
404000
middle
403000
HOLOCENE
05'00"
402000
PLEISTOCENE
401000
PLIOCENE
400000
36°07'30"N
MIOCENE
106°07'30"W
NMBGMR Open-file Geologic Map 70
Last Modified September 2014
A DIVISION OF NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY
7,000
feet ASL
6,000'
S
285
84
Qtcg2a
Qay
Cross section
D-D’
N
Tcvc
Tccu
Tcc
Tcv
Tcv
Tto
Tto
Ttch
Tcc
Tcv
Qay
Tcc
4,000'
3,000'
Rio
Chama
2,000
meters ASL
74
Tcv
5,000'
Hernandez
C'
Cross section
A-A’
Tcc
Tcv
Tcc
Tcc
Tcv
Tcv
Tto
1,500m
Tto
Ttch
1,000m