NMBGMR Open-file Geologic Map 210
Last Modified May 2012
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES A DIVISION OF NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY
106°5'0"W
401000
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Qal
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15
@m
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Kd
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Qal
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&
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o
FIGURE 1–Sinkhole in Permian San Andres Formation. Sierra Blanca is in the background.
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Qac
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Py
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o
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o
o
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Qgo
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3718000
Pag
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Qac
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5
Qac
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Qb
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3717000
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:
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Qpy
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Qpy2
Pleistocene
Neogene
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Qac
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Qa
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Qgo
Early Middle Late
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Qac
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Qpy2
Qpy2
Qpy
Qa
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Qac
Qpy
Qpy2
Holocene
Qac
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Qac
Pag
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Qpy2
Qal
Pag
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Qac
Qac
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3
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Qb
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Qal
5
Qac/
Qpi
Qes
Qgo
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Qpy
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Qb
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Qb
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Qa
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Tism
Tidm
3708000
Tidm
Tism
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o
Strike and dip of inclined bedding.
Horizontal bedding.
o
o
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Ti
Qac
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402000
403000
106°2'30"W
404000
A
A'
J
Kcc
Tism
3707000
405000
406000
33°30'0"N
J
Vertical bedding.
A'
Geologic cross section.
FIGURE 3–Partial ammonite from Cretaceous Tres Hermanos Formation, Mancos Group.
:
Base map from U.S. Geological Survey 1966, from photographs taken 1958, field checked in 1964, edited in 1966.
Polyconic porjection, 1927 North American datum,
Projected to 1927 North American datum, UTM projection -- zone 13N
1000-meter Universal Transverse Mercator grid, zone 13, shown in red
FIGURE 4–Gypsum in the uppermost Yeso Formation. view is to the north.
1:24,000
1
0.5
1000
RED CANYON
WAGON CANYON
BULL GAP SW
THREE RIVERS NW
0
1000
0
2000
3000
1 MILE
4000
5000
6000
Geologic map of the Bull Gap quadrangle,
Lincoln County, New Mexico.
7000 FEET
CARRIZOZA WEST
1
NEW MEXICO
BULL GAP
Bull
Gap
CUB MOUNTAIN
OSCURA
GODFREY PEAK
0.5
0
June 2010
1 KILOMETER
CONTOUR INTERVAL 20 FEET
Kate Zeigler 1, and Bruce Allen 2
NATIONAL GEODETIC VERTICAL DATUM OF 1929
QUADRANGLE LOCATION
Magnetic Declination
May, 2002
13º 0' East
At Map Center
Megacrystic Sills—Andesitic in composition with equigranular matrix and phenocrysts of
pyroxene. Phenocrysts are 2-5% of the rock and range in length from 1-2 mm to 1 cm.
Strike-slip fault–Showing relative horizontal separation; solid
where exposed or known; dashed where approximately located;
dotted where concealed.
50
Qac
o
106°5'0"W
Tism
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::
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o
Fine Grained Intermediate Sills—Pinkish-brown or pale-green aphanitic with very rare
phenocrysts of pyroxene or feldspar. Occasionally platy in appearance and less than 1 m in
thickness.
Normal fault–Bar and ball on downthrown side; solid where
exposed or known; dashed where approximately located; dotted
where concealed.
e
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o
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Qal
26
401000
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400000
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2
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399000
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&
Paleozoic
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Qal
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398000
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Kcc
Qac
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&
Qac
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J
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Tidm?
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e:
Tisf
Tidm?
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:
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Syenite Sill—
observed. Phaneritic texture, 2-3 m in thickness.
Yeso Formation—Very pale-reddish-brown to light-brown. Predominantly gypsum with
minor limestone/dolomite. No sandstone or mudstone beds were observed. Gypsum is
faintly laminated in places, though bedding is usually contorted. Very rarely, near-alabaster
quality gypsum was observed. Limestone beds are less than 0.3 m thick, are dark-brown-gray
in color and appear to be intensely bioturbated, though no fossils are preserved (suggesting
partial dolomitization of these units).
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:
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Kd
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Tiss
Py
Rio Bonito Member, San Andres Formation—Thin beds of dolomite with rare, medium
beds of dark-gray micrite. No fossils are preserved. Locally the unit is heavily brecciated,
probably by later karsting. Modern karst features include large sinkholes developing along
the tops of the ridges that are up to 15 m in diameter. Represents only the lower third of the
Rio Bonito Member, as no medium-bedded, dark-gray wacke-packstone beds were observed.
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3709000
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Kg Kcc
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Kt
Psr
Fine Grained Intermediate Dikes—Green to dark-green syenogabbros with pyroxene phenocrysts usually less than 1 cm in length and comprising up to 2% of the rock. Outcrop exposures tend to be short in length, never exceeding 0.75 km and usually much shorter. Also usually pervasively altered.
Trachyandesite Dike—Comprised of zoned feldspar in a matrix of feldspar and pyroxene.
Phenocrysts are plagioclase feldspar and are up to 3 mm across.
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&
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Kcc
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o
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16
Kg
18
Contact–Solid where exposed or known; dashed where
approximately located; queried where uncertain.
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Tism
Kmm
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Kt
Qac
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40
Kt
Intermediate Dikes—Vertically-oriented intrusions that are andesitic in composition with
equigranular matrix and phenocrysts of pyroxene and occasionally feldspar. Phenocrysts are
2-5% of the rock and range in length from 1-2 mm to 1 cm. In one dike, pyroxenes are up to 6
cm in length and are 10% of the rock.
Tita
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MAP SYMBOLS
3710000
Kcc
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o
8
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20
14
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21
o
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Kmm
Qa
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:
Qac
19
Qgo
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Qa
Qa
Qa
36
@m
Kg
5
8
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Qac
397000
Kg
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9
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30
Kmm
o
21
Qac
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Kd
o
Qa
Tg
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$
Qpy
396000
Qa
!!
Qa
Locally beds are bleached nearly white.
20
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6
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26
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Kt
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Kcc
Kg
15
34
Grayburg Formation, Artesia Group—
arenite/wacke with well-sorted, well-rounded grains. Heavily bioturbated such that most
original sedimentary features were obliterated though laminations and ripple laminations
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5
33°30'0"N
10
Kmd
Kmm
Pag
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Qpy
16
Qgo
o
:
Proterozoic rocks (subsurface)
Qes
o
12
Tidm
Qa
X
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o
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Tidf
Kcc
14
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Pennsylvanian, Mississippian,
Devonian, Silurian, and
Ordovician strata (subsurface)
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Moenkopi Formation—Purple-gray and consists of interbedded-pebble conglomerates and
very-coarse to fine sandstones. Sandstones are usually coarse-to very-coarse grained, but thin
beds of very-fine grained sandstone are also present. Composition varies between lithic arentures in sandstone beds are planar tabular bedding and tabular crossbedding. Rarely, high
angle trough crossbedding was observed. Grains are well rounded and range from poorly
Permian Strata
Kcc
Qes
o
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Qac
Qpy
Qes
Kcc
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Qac
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Qes
Kg
10
oo
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Qac
9
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Qac
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Qa
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Pennsylvanian
Tidm
Qa
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Qac
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o
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Qpy
3711000
Qac
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Qgo
Py
o
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11
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Qa
3708000
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14
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3709000
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Qa
Kg
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3710000
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Qa
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20
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Tisf
9
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Qa
Tisf
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19
@m
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33°32'30"N
Qal
18
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Qpy
Gravel—Well-cemented cobble to boulder conglomerate. Clasts are Sierra Blanca volcanic
fragments, as well as occasional siltstone and sandstone fragments, all of which are subrounded to well rounded. Matrix is a very coarse sandstone that is subrounded to subangular, poorly sorted with high proportion of silt and clay and more than 80% lithics. Unit is
locally incised into underlying Cretaceous strata and usually buried beneath modern deposits. Basal contact is locally an angular unconformity with Cretaceous strata.
Tertiary Intrusives
Psr
CambrianMississippian
Tisf
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Kt
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@m
Qac
Tisf
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21
Kg
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Qac
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@m
3712000
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18
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Qal
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Kcc
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Kg
o
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Kmd
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Kd
22
e
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8
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Qpy
Psr
Kg
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Qac
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Qpy
Tisf
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Kt
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Kd
8
Kd
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Permian
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Dakota Formation—
pebble conglomerates that often have faint planar crossbeds. Both sandstone and conglomerate beds frequently contain red, purple or yellow mud rip-up clasts that are well rounded.
Pag
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Proterozoic
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Triassic
^m
Mancos Shale—Lower Mancos shale consists of interbedded thin sandstone beds and darkgray shale with multiple white-to gray-white bentonite beds in the lower part. Up-section,
there are no sandstone beds and fewer bentonite layers. The Bridge Creek Beds include three
limestone units, each of which consists of a single limestone bed that is never more than 0.5
m thick. Each limestone bed is separated from the one above by less than a meter of gray
shale. The lower unit is a dark-gray (fresh), densely crystalline micrite with that is nodular
and weathers dark-yellow. Locally this unit is fossiliferous, though the majority of the material is broken shell fragments. Recently, a rare specimen of Picnodonte newberryi was
collected from this area. The second limestone is laminated dark-gray micrite and the third
limestone is similar to the first, though does not appear to contain fossils. Above the Bridge
Creek Beds is gray shale.
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Kd
10
8
3713000
Tisf
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Qal
Tertiary Deposits
Tres Hermanos Formation, Mancos Shale—Series of interbedded poorly-cemented paleyellow crossbedded sandstones and much more indurated dark-brown lithic arenites that
contain shell debris and chert fragments. The yellow sandstones are trough crossbedded
rounded grains. The dark brown sandstones are medium-to coarse-grained, subrounded,
matrix. Beds are usually massive, though occasionally display trough crossbedding. The
lower part of the unit is thick bedded, though bed thickness becomes more variable in the
upper part where the sandstone interfingers with thin dark-gray shale layers. Locally, significant accumulations of manganese have collected on bedding planes and joint surfaces, turning large parts of the outcrop to a dark-metallic-purple color and include small accumulations of boernite (?).
^m
Kmm
Tg
4
Kd
Old Gravel Deposits—Long, low mounds with flat tops that sit on the modern land surface
and consist primarily of cobbles to boulders of Sierra Blanca volcanic material. Presumed to
be the erosional remnants of material shed off the western escarpment of the northern Sacramento Mountains. Mounds have no internal stratification and no evidence of older bedrock.
Up to 2 m thick.
Kmt
Kd
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6
Qpy
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12
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28
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Qa
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Pag
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Qgo
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Qa
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Qac
@m
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Kg
Qac
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$
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Kt
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11
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$
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@m
Pag
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Kg
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o
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3
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Kg
!
Intermediate Piedmont Alluvium—Lower Holocene (?) to Middle (?) Pleistocene. Pebbly to
cobbly sand, silt, and clay, with abundant boulders of Paleozoic bedrock in northwestern
map area. Upper surfaces of unit are commonly gravely lags (desert pavements), and range
up to several meters above active drainages. Deposits are weakly dissected to extensively
stripped, depending on locality. Unit commonly exhibits pedogenic accumulation of
gypsum a few decimeters below the surface. In areas where the deposit has been stripped,
pedogenic gypsum horizons have been exposed and weathered to form a hard gypsum crust
at the surface. Up to 5 m thick or more.
Carrizozo Basalt Flow—Alkalic to transitional olivine basalt. Black to dark-gray, aphanitic,
vesicular basalt with rarely-visible phenocrysts of olivine. Texture is predominantly pahoehoe, but locally a’a textures prevail. Dated at ~5000 years old (Dunbar, 1999).
Qb
Kmd
Cretaceous
12
Mesozoic
: :
Kd
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Tg
@m
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Tg
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Qac
3711000
o
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40
22
Younger Piedmont Alluvium—Northwestern part of map area. Holocene.
Silt, sand, and clay with local accumulations (lenses) of pebbly sand. Generally
mont alluvium (Qpy and Qpi) or buries older deposits in distal piedmont areas.
Up to a few meters thick.
Quaternary Extrusives
3714000
Qac
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17
Qa
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65
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8
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Kmm
Kg
14
o
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Qpy
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Kg
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:
:o
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Qac
32
Kt
!
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Qa
Qac
Qpy
!
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J
A
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Qa
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Qa
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9
Kd
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Qa
Qpy
@m
Qgo
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Qa
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Qac
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Pag
Pag
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:
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Qa
Qb
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Qal
!
!
37
!
Qac
Qac
33°32'30"N
!
Kcc
Kt
!
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!
Qa
Qb
Qac
!
Paleocene
34
!
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Qgo
Tisf
Tism
!
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25
20
Qa
!
Igneous intrusions
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Tiss
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Eocene
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6
Pag
!
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Qac
$
Kd
!
Ti
D Cross Tongue, Mancos Shale—Dark, yellowish-gray shale with common siderite concretions that are up to 0.5 m in diameter. Occasional sandstone concretions with shell fragments
are also present. In the upper third of the unit, very thin laminar or massive fine-grained
sandstone lenses may occur, reflecting the gradational contact between the upper Mancos
and the overlying Gallup Sandstone.
and either planar-tabular bedded or massive. In places, lenses of bioturbated yellow-brown
sandstone occur that often include dense lenses of oyster and bivalve fragments, as well as
ammonites that range in size from 10 cm in diameter to over 0.3 m in diameter.
Tiss
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5
!
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!
3712000
!
Psr
!
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!
Qac
40
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Qac
!
: :
Qac
20
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Qa
:
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Qb
:
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Qb
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Qb
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30
o
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Pag
12 Psr
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Pag
!
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21
!
40
!
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!
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Qa
Qal
:
!
!
9
Qac
!
3715000
!
!
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!
!
3713000
Qb
::
!
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Pag
Psr
!
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!
!
o
o
!
!
Qac
10
!
!
:
5
!
@m
!
!
Qa
8
@m
!
o
o
!
Pag
!
Qa
!
o
!
Qac
Psr
!
Tita
!
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Qac
&
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:
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!
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Qpy
!
15
!
Qa
Qa
:
!
34
!
12
Psr
!
Qa
&
8
!
!
!
!
6
!
!
$
!
Qac
Qa
!
!
!
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!
!
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!
!
Tidf
o
Qac
!
!
Oligocene
!
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!
Qpy2
!
!
Tisf
Qac
3714000
!
Psr
Qa
Tidm
!
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!
?
!
!
Qpi
!
!
Qa
Miocene
!
& Qgo
$
!
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Tg
!
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!
Qpy
!
!
!
5
Qac
!
3716000
&
!
!
!
Qgo
Qac
!
:
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Qa
Qpy2
Qpy
!
8
Qpy2
3715000
! !
!
Kd
527
!
Qpy2
o
!
6
18
!
!
!
Qpy2
Qpy
!
!
:
Qpy
!
:
:
Qpy2
Qpy2
Qac
!
25
o
Qac
Qa
!
Pliocene
Paleogene
!
!
$
!
Qac
Qac
Qac
Cenozoic
7
o
Qa
Qac
:
Qac
33°35'0"N
$
Qgo
o
o
o
o
3716000
Qa
Qpy
Qa
Qpy2
Kt
Younger Piedmont Alluvium—Holocene to Upper Pleistocene (?). Silt, sand and clay with
locally abundant pebble to boulder gravel. Coarse-grained clasts (gravel and boulders) are
more common in areas proximal to surrounding bedrock uplands. Over most of the map
area, unit is generally structureless, pale-reddish brown, and fine grained (silt, sand, and
supported, angular to subrounded gravels. In the northwestern part of the map area, unit is
divided into older peidmont alluvium (Qpy), which is commonly capped with a moderately
Qpy2
Qgo
Qpy2
Kmd
Alluvium of Valley Floors and Adjacent Lowlands—Holocene to Upper Pleistocene (?).
Fine-grained (silt, sand, and clay) alluvium and small channels of poorly-to moderatelysorted pebbly sand. Relief between channels and surrounding alluvium is generally less than
1 m, but locally exceeds 4 m in larger arroyo cuts. Deposits are generally structureless, very
pavement development. Up to several meters thick.
?
Qpy2
33°35'0"N
sedimentary structure and fossils found in this unit include “razor oysters” and the bivalve
Cardium sp. In the lower third of the unit, medium-to thick-bedded sandstones are interbedded with thin shale intervals that occasionally include large, orange siderite concretions.
m thick or more.
!
Qpy2
3717000
Qa
Qac
Qac
Qac
!
Qpy
Qal
Qpy2
3719000
85
!
!
Qa
Qa
Qpy
3718000
6
Py
!
!
Qa
5
Qac
Qac
Qal
!
:
!
!!
o
Py
Gallup Sandstone—
sandstone is fine-to medium-grained, subrounded, moderately-well sorted, though some
!
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!
Qb
4
!
Qpy2
Kg
!
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:
:
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!
!
Qpy
Undivided Alluvium and Colluvium—Holocene to Middle Pleistocene (?). Silt, sand, gravel
and clay in various proportions, generally unconsolidated, deposited in a variety of deposiand eolian deposits on hillslopes, drainages, and dip-slopes underlain by bedrock; interfingers with differentiated alluvium (e.g., Qp and Qa) along valley floors. Older deposits may
exhibit accumulation of pedogenic gypsum and calcium carbonate. Unit also includes areas
of unmapped bedrock and differentiated alluvium. Up to a few meters thick.
:
!
!
!
!
o
:
:
o
3
!
Psr
!
!
!
o
!
!
11
Qa
Eolian Sheet Deposits—Very fine-grained sand to silt deposited by wind and subsequently
reworked by sheet flow across the surface. Ranges in thickness from less than 0.5 m to over 2
m and can include pebbles of local bedrock, as well as of Sierra Blanca volcanic material.
!
Qa
Qac
Psr
!
Qa
3719000
Qes
Py
!
Qpy2
!
!
Qpy
Qac
Crevasse Canyon Formation—Fine-to medium-grained, well-rounded, well-sorted with up
to 20% lithic fragments that include chert grains. These sandstones contain relatively abundant clay matrix and thus are generally classified as lithic wackes. The dominant sedimentary
structures are trough crossbeds, though planar tabular bedding and massive beds are also
present. Color of the sandstone varies from brown to pale-green to yellow. Muscovite mica is
a common component of the shales, which are yellow-gray and contain siderite nodules and
can be carbonaceous.
!
!
Py
!
14
11
Py
Kcc
!
!
Psr
6
Psr
!
!
29
!
!
Qpy
!
!
!
!
10
Psr
!
Alluvium—
of Permian and Cretaceous clasts, as well as abundant material from the Sierra Blanca volcanic field.
!
!
oo
!
13
Qpy
Qal
!
Qpy2
Qpy2
Psr
Qac
Cretaceous Strata
!
3720000
o
Py
Qpy
!
Qpy2
Qac
6
:
!
!
Psr
5
Py
!
!
Py
!
!
!
Qpi
o
!
!
!
!
!
!
!
!
:
:
!
!
!
:
Qpy2
Py
!
!
!
3720000
!
Psr
!
Qac
!
!
!
!
!
:
!
!
Qal
!
:
o
!
Py
!
12
!
24
!
!
33°37'30"N
!
!
!
7
!
!
!
Qpy
o
!
!
Psr
53
Qac
Qac
Psr
!
Qpi
!
407000
!
Py
!
!
Py
Psr
!
Qpy2
406000
!
:
4
405000
!
!
!
e
o
Qpy
Psr
12
11
403000
!
Psr
Qpy2
402000
o
400000
o
399000
Quaternary Deposits
404000
:
398000
o
397000
o
396000
33°37'30"N
106°2'30"W
1
New Mexico Bureau of Geology and Mineral Resources
2
Zeigler Geologic Consulting, Albuquerque, NM, 87123
New Mexico Bureau of Geology and Mineral Resources, 801 Leroy Place, Socorro, NM, 87801
Open-file Geologic Map 210
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).
New Mexico Bureau of Geology and Mineral Resources
New Mexico Tech
801 Leroy Place
Socorro, New Mexico
87801-4796
[575] 835-5490
http://geoinfo.nmt.edu
This and other STATEMAP quadrangles are (or soon will be) available
for free download in both PDF and ArcGIS formats at:
http://geoinfo.nmt.edu/publications/maps/geologic/ofgm/home.html
COMMENTS TO MAP USERS
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 may be based on any of the following: 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.
Cross sections are constructed based upon the interpretations of the author made from geologic
mapping, and available geophysical, and subsurface (drillhole) data. 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.
The map has not been reviewed according to New Mexico Bureau of Geology and Mineral Resources
standards. 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.
FIGURE 5–Outcrop of Permian Grayburg Formation (Artesia Group). View is to the north.
FIGURE 6–Crossbedding in Cretaceous Crevasse Canyon Formation.
FIGURE 2–Pahoehoe texture, Carrizozo lava flow.
SE
Acknowledgements
Funding for the mapping of Bull Gap Quadrangle was provided by the State Map Program, which
is jointly supported by the U.S. Geological Survey and the New Mexico Bureau of Geology and
Mineral Resources. I thank Dr. J. Michael Timmons for logistical support, and Stacy Timmons and
Cathie Eisen for contact information for local land owners. Land owners who graciously granted
permission for work on their property include the Hooten family and Ms. Carol McDonald. Fieldwork was conducted by standard methods, except in the few cases where land could not be
accessed adequately – in these instances, geologic data was obtained and extrapolated from previous geologic maps, air photography and adjacent geology.
5,700
5,500
5,300
5,100
4,900
4,700
4,500
4,300
4,100
A
A'
Tism
Qac Qac Qal
Qac
Qa
Qal
Qal
Qac
Qpy
Qal
Qac
Qal
Qa
Kmd
Qgo
Qal
Kcc
Kg
Psr
Kd
Kmm
Q
Qac
Kmd
Kt
Kg
^m
^m
Kmm
Py
Kd
Pag
^m
Kt
5,700
5,500
5,300
5,100
4,900
4,700
4,500
4,300
4,100