U.S. DEPARTMENT OF THE INTERIOR GEOLOGIC INVESTIGATIONS SERIES U.S. GEOLOGICAL SURVEY 3 I–2631 105°37'30" 35' 32'30" 30' 105°27'30" 32°07'30" 32°07'30" Mountain and on Wind Mountain; two additional anticlines lacking exposed igneous rocks in their cores Psa Psa Cornudas are present north of Flat Top and southwest of Alamo Mountain. Between the anticlines are a series of Py Psa Psa Psa Mountain Ph subparallel to obliquely trending synclines or structural sags. The most pronounced syncline can be 11 ° 9 Qc traced along the west side of Wind Mountain where sedimentary rocks dip as much as 60 away from Py Psa 13 the peak. The complex, locally merging and commonly curvilinear patterns defined by the traces of the Ph Ti Black Qc 6 Qaf Qc North pၤ Qaf axial planes of folds in the Cornudas Mountains bears a strong similarity to folds associated with intru- Mountain Qaf Qaf Qa Psa 14 Qaf sive rocks so well described by Hunt (1953) in his study of the Henry Mountains, Utah. ၤ




Qaf

 p Psa Psa To the north, Cornudas Mountain is within an anticline that can be traced for 12 mi (20 km) com- Ti Qfy 3000 Ku Psa pletely across the map area; the Hueco Formation is well exposed in that part of the fold that is cen- Py Py 11 Qa tered on the intrusive rocks. The anticlinal axis trends northwest on the east and folded Hueco lime- Ti Ph Psa Qa Qaf Unconformity 6 stones appear to extend beneath the east side of Cornudas Mountain. On the west, the fold deforms Ph East Qa Qaf Psa Qaf 7 Hueco limestones that overlie the intrusion; the fold axis trends west in this area but is displaced about 1 6 12 5 Wind pၤ mi (1.6 km) to the north where it merges with a north-trending structural sag or syncline before reach- pၤ Qc 5 Qc plift Mtn. ing the western map boundary. Spatial relations between the Cornudas Mountain intrusive and the brian lrocks u of Psa Psa










 5000 adjacent folded rocks suggest that an elongate intrusive body underlies the entire anticlinal fold and that Ph 4 Qaf Psa PrecamPederna Flat Top Qc Psa Psa the exposed Cornudas intrusive is an irregular-shaped, sill-like body that plunges gently west, yet is bulg- Py Psa ingly discordant on the east (fig. 2); Hunt (1953) might have termed this apophysis of the underlying 3000 Ti 500 Ph Ph 0 Qc 13 intrusive a sphenolith. 5000 Py 6 13 pၤ 17 Qaf Psa Wind Mountain is the core of a dome in which dips of enclosing sedimentary rocks of the Hueco ၧၤu Qc 7 Qa pၤ 3000 Psa Formation are locally more than 60°. A structural sag appears to separate Deer Mountain on the west SEA ၤ 3000 LEVEL p ၤ from the main part of the dome; however, the Deer Mountain intrusive also intruded the Hueco and is p Qaf Alamo  



 12 structurally in the core of a west-trending anticlinal flexure that is a part of the Wind Mountain dome Mountain Psa SEA 5 Psa Ku LEVEL Qaf (fig. 2). The similarity in composition of the Wind and Deer Mountains intrusives suggests that they are SEA 0 6 7 petrologically related as well. The Wind Mountain dome cannot be traced east of the peak. The Wind LEVEL Ku 5000 FEET 13 5 Psa Psa 13 7 Mountain intrusive has been interpreted as a laccolithic intrusion (McLemore and others, 1996); howev- Ti Ph 1 South 3 Psa Ph Qaf 4 er, geologic and geophysical relations mapped during this and a previous study (Nutt and others, 1997) Ti 3000 4 Qaf argin 2 Qa 7 9 suggest that an alternative interpretation is justified. There is no evidence that sedimentary rocks floor ၧၤu Qaf 10 Qfy 21 Qfy the intrusion; all sedimentary host rocks are strongly deformed adjacent to the intrusion and dip steeply Py ၧၤ 3 4 7 Qaf u pၤ










Qaf away from the peak. Foliation within the Wind Mountain intrusive defines a circular pattern that is SCALE IN MILES SEA Psa 23 LEVEL 10 4 6 Qfy mimicked by the enclosing sedimentary rocks. The aeromagnetic signature at Wind Mountain is the 5000 Psa 4 est-facing,of Pedernal faulted uplift m 5 8 strongest, most prominent magnetic anomaly in the Cornudas Mountains (Nutt and others, 1997) even W 14 Psa EXPLANATION 4 though topographically similar peaks are present; all other peaks are clearly floored by sedimentary 3000 Qc 12 13 rocks and, based on the magnetic signature, lack the lithologic mass of Wind Mountain. The Wind Ti Tertiary intrusive rock Ph Permian Hueco Fm. Qaf Qaf Mountain intrusive appears to be a steep-sided plug that extends downward to its intersection with a Ku Cretaceous sedimentary rock ၧၤu Pennsylvanian to Cambrian rock parent intrusive body that underlies the combined Wind-Deer Mountains anticlinal flexure. Hunt (1953) 16 Qa Psa Qaf SEA 7 described intrusive forms similar to Wind Mountain as bysmaliths. Psa Permian San Andres Fm. pၤ Precambrian rock

 5
 6

 9  3
4





 LEVEL An anticlinal, convex-northward upwarp is present north of Flat Top. The fold plunges west and Tqs Qa Qa Py Permian Yeso Fm. 12 Qfy 3 terminates near Alamo Mountain; on the east it appears to merge with and become a part of the Wind- West Qa Qfo 14 Qfy 15 Psa Deer Mountains anticline. A second anticlinal flexure is mapped southwest of Alamo Mountain; the fold Figure 2. Schematic fence diagram showing stratigraphic, structural, and intrusive relationships discussed in text. 10 Qaf can be traced southeast at least 7 mi (11 km) into Texas. Based on the direct correlation of anticlinal Qfy Qfo 21 Ti 2 Qaf Qaf 10 flexures and doming with known intrusive rocks, we suggest that these two additional upwarps are also 17 6 23 10 14 12 33 7 cored by igneous rocks. 15 4 Qaf Qaf Ph Synclines mapped in the Cornudas Mountains appear to be related to igneous intrusions as well. 4  Psa
 




Qa  10 Tqs They occur as partial ring structures around Wind Mountain, as structural sags above and between bur- 10 11 ied intrusive bodies, and as paired anticline-syncline accommodation folds formed in response to dilation 16 25 Qfy Ph 13 8 of intruded sedimentary rocks. 106°00' 105°00' Qc Peaks in the map area other than Cornudas Mountain and Wind Mountain do not appear to be 7 48 Qfy 7 Psa

0 associated with strongly deformed sedimentary rocks. Alamo Mountain, San Antonio Mountain, Chatt- ° –992 3500 21 4 32 30' Qfy field Mountain, Black Mountain, and Flat Top are similar to one another in that they are concordant Qaf 9 Qa 16 –2500 22 4 Tqs Qaf and clearly sills or laccoliths, and, unlike Wind and Cornudas Mountains, they were injected into sedi- –1500 Qc T









 6 mentary host rocks at or above the Permian-Cretaceous unconformity (fig. 2). San Antonio Mountain,

–500 9 235 IF 3000 –1000 500 2500 8 Qa Psa perhaps the only true laccolith of the Cornudas Mountains and only partly exposed in the south-central –2000 L Psa 19 2000 14 1000 8 Qao part of the map area, is floored by basal Cretaceous rocks (Kues and Lucas, 1993). Chattfield Moun- –3000 500 1500 Qfy 14 1 UP Qaf tain, at least on the north where exposed in the map area, also is underlain by flat-lying Cretaceous stra- –3500 Qaf 19 Ph 2000 5' Qfy 5' ta. Black Mountain, a multiple sill complex east of Wind Mountain, was emplaced in part directly above 2500 1000 15 Ph 6 850 3000 10 6 10 Ph the unconformity as well as higher in the Cretaceous section. The Flat Top sill is underlain by the San 12 10 8 Qc Py Qc Andres Formation; no Cretaceous rocks were observed on this peak. The stratigraphic position of the L Qaf



 4






 8 17 3 unconformity east of Flat Top (north of Wind Mountain) as well as on the west (beneath Alamo Moun- A Psa Qc Qaf tain) relative to the statigraphy at Flat Top suggests that the Flat Top sill was intruded along or very near 1664 N Psa Qfo Qa R Qfy the Permian-Cretaceous unconformity. E 5 Qc 8 Qfy The Alamo intrusion is perhaps the most complex of the stratigraphically higher intrusions (fig. 2). 1214 1935 D Qfy E 10 11 The intrusive body is discordant on the north where it probably intruded gently west-dipping limestones P 24 7 Qaf Qa 3 of the San Andres. Along the south and west base of the peak, Cretaceous rocks are exposed. Flow 481 1560 10 9 foliation within the intrusive is complex. On the north flank, foliation dips steeply north; midway Qaf














 between the north flank and the crest of the peak, foliation is gently inclined to the north. Directly Ph 5 Qa beneath the crest of the peak, the foliation steepens whereas at the crest the attitude of the foliation 5 Qa Qa Psa 4 NEW MEXICO Psa 13 again becomes nearly flat lying. The contemporary morphology of the peak, as viewed from the north- 32°00' Qa –2933 Qfy west, reflects the abrupt changes of foliation attitude. Hornfelsed Cretaceous rocks rest on the intrusion TEXAS 3 Py Psa 0 20 MILES Qao on its north side (shown as Km) suggesting that the present exposed upper surface of the igneous rocks 5 probably represents the exhumed upper contact of the intrusion. As such, Alamo Mountain appears to 2280 1232 Psa 16 Qfy 18 Qaf 0 20 KILOMETERS 14 represent a steeply inclined, thick, east-trending dike on the north where it intruded Permian strata. When the dike encountered the Permian-Cretaceous unconformity, it spread laterally to the south as a 
Qa  12

Qa Ph



Figure 3. Structure contour map drawn on top of Precambrian basement showing location of buried Pedernal uplift concordant intrusion before it bulged, thickened, and folded overlying Cretaceous rocks; it then con- Qfy Qaf with respect to Cornudas Mountains (pink). Contour interval 500 ft; datum is mean sea level. Solid dot, well, Psa 8 21 18 cordantly invaded Cretaceous strata farther to the south before abruptly terminating at its present loca- Qaf showing depth. Dashed line, fault; bar and ball on downthrown side. Modified from King and Harder (1985). Qfy 8 tion. In a crude way, Alamo Mountain appears to represent an incompletely formed laccolith with its 4 Qc Psa 7 northern half undeveloped (fig. 2). Hunt (1953) did not describe an intrusive form quite like Alamo 12 Qa Qc 9 Mountain although he did suggest, following Daly (1914), that such an intrusive form could be called a Qc Qa Psa 9 Qao Qfy Qa chonolith. 105°40' 25 17 17

3





 Faults 15 Qfy Ph Qaf Qa 12 11 40 Qc Qaf Qfy The Cornudas Mountains are near the western edge of the Salt Basin graben (fig. 1), which is the easternmost structure related to Basin and Range tectonism and shows evidence of Quaternary fault Qa Qaf 12 Psa Qaf Qc Qa movement (Goetz, 1980). In contrast, the Cornudas Mountains are cut by rare faults in which the offset 16 7 Qaf is typically 15 ft or less (4.6 m). Apparently the Cornudas Mountains are within a stable block bounded 12 Qfy 12 75 11 by segments of the late Cenozoic Rio Grande Rift to the west and east. Several of the small faults are Qa 24 18 Psa 12 3 6 Qao Qfy Qao 8 Qa intruded by dikes related to the larger intrusions of the area. We interpret the faults to have formed




Psa  Qaf


 14








 mainly in response to deformation of host sedimentary rocks during intrusion of alkaline rocks. Psa 9 5 13 5 Psa Qfy 17 5 10 17 Td PRE-PERMIAN FAULTING 6 4 Qaf Qaf Ph In Pennsylvanian time, New Mexico and adjacent Texas and Colorado were the sites of numerous Qaf Psa 3 59Qc 14 uplifted intracratonic basement blocks of the ancestral Rocky Mountains (Kluth and Coney, 1981). Py 25 Td Most of these uplifts and adjacent basins in New Mexico trended north; one of the larger crustal blocks, 17 44 3 18 10 9 Qaf Qc 15 16 9 3 the Pedernal uplift, can be traced on the surface from central New Mexico southward into the Sacramento Mountains in eastern Otero County (fig. 1). From the Sacramento Mountains southward,



 




 Qfy 9 Qc Td Qa 16 the uplift is buried beneath Permian rocks that now underlie the Otero platform. Basement faulting, Psa 78 Psa Qaf Qaf 80 11 9 Psa stratigraphic pinchouts, and syntectonic sedimentary deposits associated with the uplift are best exposed 5 Qfy Psa Qc in the Sacramento Mountains near Alamogordo, N. Mex. (Pray, 1959; Kottlowski, 1963; Bauer and Lozinsky, 1991). To the south, similar geologic features associated with the uplift have been detected in 12Qfy 13 Qaf 20 6 10 exploratory oil wells drilled on the Otero platform (Black, 1975). 18 Qfy Psa 12 Qaf Structure contours drawn on the top of the buried Precambrian of the Otero platform indicate that Qfy Tas Qaf 5 Qaf 12 Qa Psa the Cornudas Mountains are located near the western edge of the buried Pedernal uplift (Woodward and







  4 16 others, 1975; Foster, 1978; King and Harder, 1985). Geologic cross sections drawn across the Otero 12 11 Tp 14 16 platform by Black (1975), particularly his section C–C’ drawn through the northern part of the Cornu- Psa Td 16 Tas das Mountains, show the beveled top of the buried pre-Permian uplift. In section C–C’, the well drilled Psa 2 Qc Qaf Qfo Ti 13 east of the Cornudas bottomed in Permian strata resting directly on Precambrian rocks at 2,280 ft (684 20 12 Py Qfy Psa 11 Kc Qaf Qt m) above sea level; the well on the west penetrated Permian as well as older Paleozoic rocks and Qfo Tas Qfy encountered Precambrian basement nearly 2,000 ft (600 m) lower, at an elevation of 481 ft (145 m) Qt Kma Qt Qa Qaf (King and Harder, 1985). The faulted, western edge of the Pedernal uplift, as shown by Black, is locat- 7 




 15






Qc ed between these two wells; in this cross section the Cornudas Mountains are shown as laccolithic intru- Td 2'30" 8 Psa Qa 6 Tps 2'30" sions localized along a minor fault located about 2 mi (3.5 km) west of the faulted edge of the uplift. Qa Tps Qfy Ti Qao Qa Geologic mapping and geophysical investigations conducted by Nutt and others (1997) suggest Tp 4 Kc Kc that the western, faulted edge of the Pedernal uplift lies beneath or west of the Cornudas Mountains. Qls 3 Qa 25 Qao Psa 43 Qfy Kc Kma 8 Geologic evidence for the location of the buried uplift margin is derived from regional variations in the Qls thickness of the Permian Yeso Formation. In the Cornudas Mountains, the Yeso is only 100 ft (30.5 8 Qt Qt Tas 3 Ph Psa QTp Qt Kma Qc Qa m) thick. In cross sections constructed by Black (1975, C–C’), exploratory oil wells drilled 10 mi (16 12 Qt Qa QTp
Qa QTp













 8  4
 km) east and 5 mi (8 km) northwest of the Cornudas encountered a much thicker Yeso: about 850 ft QTp Kc 3 7 Qt Qfy 14 Qfo (255 m) thick on the east and nearly 900 ft (270 m) thick on the west (King and Harder, 1985). The 12 4 Ph Tps Qt Qfy Qt explanation for this anomalously thin Yeso section is speculative. The Yeso is exposed only as upturned Qls Qfy Kc 6 Py Psa Qfo QTp strata between the Hueco and San Andres around the Wind and Deer Mountains and Cornudas Moun- 12 Qfy Psa 24 28 Kma Qaf 7 Psa 15 Psa tain intrusive centers. Given that gypsum flows at the slightest provocation and is also quite soluble, it is Tp 3 Qaf 7 7 52 9 Qt 37 3 7 12 Qls possible that the thinness of the formation is the result of deformation related to intrusion and (or) disso- Tp lution due to magmatic fluids. Arguing against such an interpretation is the noticeable lack of strong Km Qt Qfy 9 Ph 50 Ph 9





Qfo














8
 

folding, contorted bedding, and brecciation of the Yeso and the overlying San Andres and the paucity of 27 Td 16 Py Td 10 28 13 Qt evidence of magmatic fluids. Alternatively, thinning of the Yeso to about 100 ft (30.5 m) in the Cornu- Td Qls 8 Tp das Mountains may likely be due to abrupt gradation and intertonguing with the overlying San Andres 11 Qc Qa Qt 15 8 14 16 4 (see Black, 1975, p. 328–329); equally likely is the possibility that the formation pinches out against, 16 4 24 7 3 Td Ph QTp over, and across an elevated Precambrian high—the uplifted Pedernal massif. Abrupt thickening of the

20 6 65 Qt Kma Yeso to the west, and the fact that the entire Cambrian through Pennsylvanian section (encountered in Kc 4 Ph the wildcat well) rests directly on Precambrian rocks that are nearly 2,000 ft (600 m) deeper than to the Qfy 12 26 5 23 Ph 62 east of the Cornudas Mountains, suggest that the major west-bounding fault of the Pedernal uplift is







Qca 



Qca







 

Psa 6 Psa Kc more correctly interpreted to be located west of or beneath the Cornudas Mountains. Tns 23 Tns1 QTp 10 Qfy Qfy 9 Geophysical evidence for an abrupt change in the character of the subsurface rocks lies in aero- 7 Psa Qls 65 Tns2 Ts Qt magnetic anomalies and audio-magnetotelluric (AMT) soundings conducted across the Cornudas Moun- Qls Qaf Ph 50 23 46 5 tains (Nutt and others, 1997). The intrusive rocks in the subsurface of the Cornudas Mountains appear Qfy 11 29 Psa 18 3 Qa Ph 11 4 to be concentrated at or near the unconformity between the sedimentary rocks and the underlying Pre- Qfy Psa 26 Py 7 Qao 74 65 Qao cambrian crystalline basement. That unconformity is interpreted from the aeromagnetic data to be 12 about 2,200 ft (660 m) beneath the surface and at an elevation of about 3,000 ft (900 m) above sea Qls




























33 11 

Qfo 15 Py Qc 42 level. Similarly, ATM soundings detected highly resistive rocks directly east of the Cornudas Mountains 4 52 Qaf 11 10 Qao that contrast markedly with a layered rock sequence detected on the west. The interpretation offered Qc Psa 17 Tns 14Qc 3 36 here is that the Precambrian basement is much nearer the surface directly east of the Cornudas Moun-

Qca 32 tains than on the west. 7 Qaf 2 Qt In their basement structure contour map of the Otero Platform, King and Harder (1985, fig. 5) Qaf Qfy have drawn a major fault in the area of the Cornudas Mountains. Projection of that fault to the surface 8 Psa Py Qao Qaf Qa places it between Alamo and Wind Mountains. We would amend their structure contour map only by 17 Qfy Qt


 21




























Ph









 Qc Qfy extending the 1,500-, 2,000-, and 2,500-ft (450, 600, and 750 m) basement contours farther south, 8 Ph 18 Qao Psa 47 beneath the Cornudas Mountains and into Texas, as shown in figure 3. We would amend Black’s cross Qa Qaf section C–C’ to show elevated Precambrian basement directly beneath the Cornudas Mountains and Psa Qc 42 6 4 Qaf suggest that intrusion of these rocks, rather than being controlled by a relatively minor fault, was con- 6 Qc Ph 17 Qca Psa trolled by a major fault or fault system located along the western margin of the Pedernal uplift (fig. 2). 11 12 Psa Psa Py 9 59 REFERENCES CITED Qa Qaf Qa 5

  























 9





 Anderson, O.J., 1994, Geologic map of New Mexico: New Mexico Bureau of Mines and Mineral 9 Qa 13 Psa 14 8 Psa Qa Qaf Resources, Open-File Report 408–A, scale 1:500,000. Qls Qls 8 Barker, D.S., and Hodges, F.N., 1977, Mineralogy of intrusions of the Diablo Plateau, northern Trans- Qaf Psa Qc 18 Psa 22 Qc 9 Qaf 46 Qfy Kc Pecos magmatic province, Texas and New Mexico: Geological Society of America Bulletin, v. 88, Qaf 16 27 Qaf 12 55 p. 1428–1436. Qc Psa Kc 15 Psa Psa 7 20 Barker, D.S., Long, L.E., Hoops, C.K., and Hodges, F.N., 1977, Petrology and Rb-Sr isotope geo- Qaf QTpQt Qaf 9 chemistry of intrusions in the Diablo Plateau, northern Trans-Pecos magmatic province, Texas and Qc 10 Kc 12 Qc Qa New Mexico: Geological Society of America Bulletin, v. 88, p. 1437–1446.




























Kma QTp Tp 19  Qc 17 Qls Barnes, V.E., 1975, Geologic atlas of Texas, Van Horn–El Paso Sheet: University of Texas at Austin, Psa 11 Qls Qt Tps Psa Bureau of Economic Geology, scale 1:250,000. Qc Psa QTp Qt 14 Qt Qa Qfy 18 Bauer, P.W., and Lozinsky, R.P., 1991, The Bent dome—Part of a major Paleozoic uplift in southern Psa Qaf Tp Qaf Psa Psa Qc Qa Qa Kc New Mexico, in Barker, J.M., Kues, B.S., Austin, G.S., and Lucas, S.G., eds., Geology of the Qaf 20 Qaf Qc Psa Kc 9 Sierra Blanca, Sacramento and Capitan Ranges: New Mexico Geological Society Guidebook 42, ° Kma Kc 32 00' 32°00' p. 175–182. 105°40' 37'30" 35' 32'30" 30' QTp 105°27'30" 11 Black, B.A., 1975, Geology and oil and gas potential of the northeast Otero platform area, New Mexi- 


 



 44 50 10° 32 co, in Seager, W.R., Clemmons, R.E., and Callender, J.F., eds., Las Cruces Country: New Mexi- Base from U.S. Geological Survey, SCALE 1:24 000 Geology by J. Michael O'Neill and Constance J. Nutt, 1996–1997; Alamo Mountain, Cornudas Mountain, 1975, 11/ 2 0 1 MILE and Clabaugh (1941), Timm (1941), Zapp (1941), and co Geological Society Guidebook 26, p. 323–333. McVeigh Hills, 1970. NEW MEXICO 10 McLemore and others (1996). Clabaugh, S.E., 1941, Geology of the northwestern portion of the Cornudas Mountains, Otero County, 62 Geology digitized by Esther L. Castellano New Mexico: Austin, Texas, University of Texas at Austin M.S. thesis, 66 p. Projection: Transverse Mercator (Alamo Mountain, 1.50 1 KILOMETER 11 Cornudas Mountain), Polyconic (McVeigh Hills). TIC NORTH Editing and digital cartography by Alessandro J. Donatich Daly, R.A., 1914, Sills and laccoliths illustrating petrogenesis: International Geological Congress, Cana- TRUE NORTH

GNE 24 27 3 da, 12th Session, Congressional Report, p. 189–204. MA Manuscript approved for publication March 26, 1998 1927 North American datum 4 CONTOUR INTERVAL 10 FEET MAP LOCATION Foster, R.W., 1978, Oil and gas evaluation of the White Sands Missile Range and Ft. Bliss Military Res- NATIONAL GEODETIC VERTICAL DATUM OF 1929 4 12 APPROXIMATE MEAN ervation, south-central New Mexico: New Mexico Bureau of Mines and Mineral Resources, Open- DECLINATION, 1998 16 7 File report 92, 130 p. 6 Goetz, L.K, 1980, Quaternary faulting in Salt Basin graben, West Texas, in Dickerson, P.S., Hoffer, 4 6 40 8 J.M., and Callender, J.F., eds., Trans-Pecos region, southeastern New Mexico and West Texas: ° 8 106 105° CORRELATION OF MAP UNITS Qaf Alluvial and fluvial deposits (Holocene)—Sand, silt, clay, and pebble to cobble gravel deposited in Ts Syenite porphyry (Oligocene)—Syenite porphyry exposed in upper parts of Wind Mountain, as Psa San Andres Formation (Lower Permian)—Medium-gray to light-olive-gray dolomite and dolomitic east; the undifferentiated Leonardian limestones overlie the Hueco on the south and west. The Hueco in Texas is New Mexico Geological Society Guidebook 32, p. 83–92. narrow stream channels and on broad alluvial slopes at base of low hills and mountain fronts. mapped by McLemore and others (1996). Fine grained; consists of potassium feldspar, albite, limestone overlain by dark-gray limestone; lower dolomitic rocks are fine to medium grained correlative to the Hueco and Yeso combined in New Mexico. The Victorio Peak and Leonardian limestones in Hunt, C.B., 1953, Geology and geography of the Henry Mountains region, Utah: U.S. Geological Sur- New 13 QaQaf Qfy Qt Qc Qca Holocene Generally less than 15 ft (4.5 m) thick aegirine, sodic amphibole, biotite, analcime, and trace amounts of magnetite and thin to medium bedded, and contain medium-gray chert nodules and stringers; sandstone Texas are equivalent to the San Andres in New Mexico. 15 Neither the Yeso nor San Andres Formations are recog- vey Professional Paper 228, 234 p. Mexico



Qfo Qao QUATERNARY Qfy Young alluvial fan deposits (Holocene)—Poorly sorted silty sand and gravel deposited in small Tps Porphyritic nepheline syenite (Oligocene)—Dark-gray-green, fine- to medium-grained, porphyritic and shale lenses are most abundant in middle part 6 of dolomitic section. Basal dolomitic lime- nized on the Texas geologic map. 4 King, P.B., 1934, Permian statigraphy of Trans-Pecos, Texas: Geological Society of America Bulletin, Qls Pleistocene 8 Texas alluvial fans along valley margins and around hills and mountains; locally includes minor colluvi- nepheline syenite. Phenocrysts consist of euhedral anorthoclase as long as 1 in. (2.5 cm) in stone is locally pisolitic and vuggy and contains layers of coquina and intraformational conglom- The complex stratigraphic relationships between the various Permian formations of southern New Mexico v. 45, p. 697–798. S QTp

a um (Qc). Maximum thickness unknown groundmass of anorthoclase, clinopyroxene, biotite, nepheline, and analcime. Well-foliated erate. Dark-gray massive limestone, restricted to uppermost exposures in map 17 area, is conspic- are summarized by Kottlowski (1963); stratigraphic pinchouts, abrupt lateral lithologic gradations, and stratigraphic King, W.E., and Harder, V.M., 1985, Oil and gas potential of the Tularosa Basin–Otero platform–Salt Pliocene 7 c 16 Qt Talus deposits (Holocene)—Unsorted, unstratified angular pebbles to boulders as wide as 30 ft (9.2 rocks characterize exposures on Black and San Antonio Mountains uously fossiliferous. Formation forms erosion-resistant ledges and has a maximum exposed younging from west to east characterize the Permian section. The Yeso Formation 3 in the southern Otero platform Basin graben area, New Mexico and Texas: New Mexico Bureau of Mines and Mineral Resources, r Area of ? a m); covers flanks of steep slopes of hills and mountains underlain by resistant bedrock thickness of about 500 ft (150 m) Circular 198, 36 p. m figure 1 Tqs Quartz-bearing syenite (Oligocene)—Medium-gray, weakly foliated, granoblastic to porphyritic grades abruptly to the south into carbonate rocks of the Victorio Peak Formation, which in turn grade into the Py 5 9 e Qc Colluvium (Holocene)—Weakly to strongly cemented caliche soil developed in residual deposits of syenite composed of tabular, euhedral anorthoclase, subhedral clinopyroxene, biotite, and inter- Yeso Formation (Lower Permian)—Interlayered gypsum-rich laminated claystone 10 locally enclosing dark, organic-rich calcareous mud of the Bone Springs Formation (Black, 1975). The upper San Andres Forma- Kluth, C.F., and Coney, P.J., 1981, Plate tectonics and the ancestral Rocky Mountains: Geology, v. 9, n t Tns sand, silt, clay, and angular pebbles and cobbles; most commonly mantles the San Andres For- stitial quartz. Exposed at Cornudas Mountain. K-Ar age of biotite is 33.9 Ma dark-gray gypsum nodules; yellow-white, sugary-textured limestone; coarse-grained gypsum; tion of New Mexico becomes younger eastward into the Guadalupe Mountains where it pinches out southward p. 10–15. o P 12 e
Ts  mation (Psa) in northwestern part of map area, which is drained by tributaries of Shiloh Draw Tp Phonolite (Oligocene)—Medium-gray-green, aphanitic rock composed mainly of alkali feldspar, red to green shale and claystone; and orange-tan to red and red-brown, medium-grained 6 quartz into Delaware basin sediments (Pray, 1988); the lower part intertongues with the Victorio Peak as does the under- Kottlowski, F.E., 1963, Paleozoic and Mesozoic strata of southwestern and south-central New Mexico: M d Tns1 Tns2 e to the north. Thickness generally less than 1–2 ft (0.3–0.6 m) sandstone. Most exposures are restricted to top of unit where red to green shale directly New Mexico Bureau of Mines and Mineral Resources, Bulletin 79, 100 p. o nepheline, clinopyroxene, and riebeckite. Locally contains xenocrysts of olivine, clinopyrox- lying Yeso (Black, 1975). The three distinct Permian units mapped in the Cornudas Mountains appear to con- 33° r u n TERTIARY Qca Colluvial and alluvial deposits, undivided (Holocene)—Colluvium (Qc) that is partly reworked and underlie the San Andreas Formation (Psa). Maximum exposed thickness about 100 ft (30.5 m) Kues, B.S., and Lucas, S.G., 1993, Stratigraphy, paleontology and correlation of Lower Cretaceous a ene, and biotite. Phonolite of Chattfield Mountain, Flat Top, and Alamo Mountain shows well- form best with nomenclature followed in New Mexico. The lowermost limestones exposed in the map area are n l Tps 9 13 t u dissected by intermittent streams infilled with young alluvium (Qa); restricted to south-central developed flow foliation. K-Ar age of biotite from Alamo Mountain is 36 Ma. On western and Ph Hueco Formation (Lower Permian)—Dark-gray, fine-grained, thin- to medium-bedded, fossilifer- likely equivalents of the Hueco Formation (Kottlowski, 1963). The Hueco is in sharp contact with the overlying, exposures in southeastern New Mexico, in Love, D.L., and others, eds., Carlsbad Region, New a p Td i l Ti Oligocene 14 RIFT n if part of map area, which is drained by tributaries of University Draw to the south southern Alamo Mountain unit Tp is platy phonolite with foliation dipping at a low angle to ous limestone containing conspicuous dark-gray to black chert nodules and stringers. Maxi- anomalously thin section of gypsum, green11 and red shale, and pale-gray limestone of the Yeso Formation. The Mexico and West Texas: New Mexico Geological Society Guidebook 44, p. 245–260. s t Tqs RIO GRANDE Qfo Old alluvial fan deposits (Holocene and Pleistocene)—Poorly sorted silty sand and gravel deposit- underlying sedimentary bedding (denoted by pattern) mum exposed thickness less than 100 ft (30.5 m) Yeso has not been reported south of Cornudas and appears to pinch out abruptly southward. The Yeso is over- McLemore, V.T. and Guilinger, J.R., 1993, Geology of mineral resources of the Cornudas Mountains, 6 14 G Tp ed in dissected, abandoned alluvial fans that no longer receive sediment. Dissection probably Tas Nepheline-bearing augite syenite (Oligocene and Eocene)—Gray, medium-grained, equigranular lain by a marine, near-shore, shallow-water deposit of carbonate rocks and sandstone that grade upward into thin- Otero County, New Mexico and Hudspeth County, Texas, in Love, D. L., and others, eds., Carls- u related to Pleistocene faulting to the east in the Salt Basin graben adjacent to Guadalupe Moun- nepheline-bearing augite syenite. Consists of anorthoclase, plagioclase mantled by anortho- Contact—Dashed where approximately located; dotted where concealed to medium-bedded dolomitic limestone and dolomite which we correlate with the San Andres Formation. The San bad Region, New Mexico and West Texas: New Mexico Geological Society Guidebook 44, p. a  
d Otero a Tas tains. Maximum thickness unknown clase, augite, biotite, and interstitial nepheline and analcite. Small body, in part covered by unit Andres in the western part of the map area grades laterally into Leonardian limestones, probably the Bone 145–153. l Eocene platform u Qao Old alluvium (Holocene and Pleistocene)—Dissected terraces underlain by sand, silt, clay, and Qaf, in Chess Draw. K-Ar age of biotite is 36.8 Ma Fault or prominent fracture—Dotted where concealed. Bar and ball on downthrown side where Springs Limestone (King, 1934) of the Diablo platform; on the east, the formation appears to grade into the Vic- McLemore, V.T., Lueth, V.W., Pease, T.C., and Gulinger, J.R., 1996, Petrology and mineral resources p Brokeoff Intrusive contact relative movement known; displacement on the order of 15 ft (4.6 m) or less e pebble to cobble gravel; preserved as small, isolated hills 3–10 ft (0.9–3 m) above active stream Td Dike (Oligocene and Eocene)—Mafic dikes mainly restricted to the Chess Draw area torio Peak carbonates, the bank-ramp facies of the Capitan reef complex (Pray, 1988). of the Wind Mountain laccolith, Cornudas Mountains, New Mexico and Texas: Canadian Mineral- Mtns. Cornudas Mtns. M valley floors Syncline—Showing direction of plunge where known. Dashed where approximately located; dotted Cretaceous sedimentary rocks, also present in the map area, are exposed only where they are overlain by or ogist, v. 34, pt. 2, p. 335–347.

o Kma Lower Qls Landslide deposits (Pleistocene)—Angular fragments of bedrock mixed with soil, or heterogeneous Ti Tertiary intrusive, undifferentiated (Oligocene and Eocene) where concealed. Synclines formed during intrusion of Tertiary igneous rocks adjacent to resistant igneous bodies at Alamo, San Antonio, Chattfield, and Black Mountains. Cretaceous rocks Nutt, C.J., O’Neill, J.M., Kleinkopf, M.D., Klein, D.P., Miller, W.R., Rodriguez, B.D., and McLemore, 32° u New Mexico Km CRETACEOUS Salt Basin n Cretaceous mixtures of boulders and finer grained material derived from adjacent steep hillslopes; charac- consist of basal conglomerate and associated sandstone, siltstone, and limestone and are remnants of a sedimenta- V.T., 1997, Geology and mineral resources of the Cornudas Mountains, New Mexico: U.S. Geo- t Kc SEDIMENTARY ROCKS Anticline—Showing direction of plunge where known. Dashed where approximately located; dot- Hueco graben a Texas terized by irregular-shaped, hummocky topography and numerous closed depressions. Land- ry section that once covered the area. The variable thickness of the lowermost Cretaceous Campagrande Forma- logical Survey Open-File Report 97–282, 46 p. i Mtns. Dell n ted where concealed. Anticlines formed during intrusion of Tertiary igneous rocks slides mainly confined to areas underlain by Cretaceous sedimentary rocks preserved adjacent [Nomenclature for Permian sedimentary rocks exposed in the Cornudas Mountains follows the terminology used tion and Cox Sandstone (Kc) suggests that the pre-Cretaceous depositional surface was locally irregular. Areas of Pray, L.C., 1959, Stratigraphy and structure of the Sacramento Mountains, in Sacramento Mountains El Paso City s Unconformity 14 to middle Tertiary igneous intrusions on the New Mexico State geologic map of Anderson (1994)] Strike and dip of bedding Cretaceous outcrop are coincident with landslide deposits (Qls) and suggest that during late Tertiary erosion of the of Otero County, New Mexico: Permian Basin Section, Society of Economic Paleontologists and Diablo Psa QTp Pediment alluvium (Pleistocene and Pliocene?)—Angular boulder to cobble gravel set in finer southern Otero platform, the less resistant Cretaceous strata slumped along the edges of the more resistant igne- Mineralogists and the Roswell Geological Society Guidebook, p. 86–130. platform Kma —Yellowish-tan to light- 52 grained matrix and deposited on gently sloping surfaces; preserved as isolated, flat-topped Muleros and Mesilla Valley Formations, undivided (Lower Cretaceous) Strike and dip of foliation ous rocks. ———1988, The western escarpment of the Guadalupe Mountains, Texas, and day two of the field EXPLANATION Lower gray, nodular, fossiliferous limestone and minor shale and siltstone (Muleros) overlain by poorly 20 MILES Py PERMIAN deposits on flanks of Alamo, Black, and Chattfield Mountains and Flat Top at elevations Tertiary and Quaternary surficial deposits are common in the map area and consist mainly of calcium seminar, in Reid, S.T., Bass, R.O., and Welch, Pat, eds., Guadalupe Mountains revisited, Texas 0 Normal fault—Bar and Permian exposed brownish-tan to orangish-tan sandstone and siltstone (Mesilla Valley). Maximum between 5,100 and 5,700 ft (1,530 and 1,710 m). Appears to be continuous with perched Platy phonolite (Tp) with foliation dipping at a low angle to underlying sedimentary bedding carbonate-cemented colluvium, alluvial and fluvial deposits, and ephemeral stream channel deposits. Perched and New Mexico: West Texas Geological Society Publication 88–84, p. 23–31. ball on downthrown side exposed thickness about 100 ft (30.5 m) Ph pediment gravels preserved 1 mi east of Chattfield Mountain at elevations near 4,900 ft (1,470 on western and southern Alamo Mountain gravels (QTp) of probable Pliocene-Pleistocene age are preserved adjacent to many of the peaks of the Cornudas Schreiner, R.A., 1994, Mineral investigation of Wind Mountain and the Chess Draw area, Cornudas 0 32 KILOMETERS Kc —Yellowish- Anticline m) Campagrande Formation and Cox Sandstone, undivided (Lower Cretaceous) Mountains. Mountains, Otero County, New Mexico: U.S. Bureau of Mines, MLA 26–94, 46 p. orange siltstone and minor cream-white, fine-grained limestone are the oldest Cretaceous rocks GEOLOGY Timm, B.C., 1941, The geology of the southern Cornudas Mountains, Texas and New Mexico: Austin, IGNEOUS ROCKS exposed in map area. The interbedded siltstone and limestone are no more than about 15 ft IGNEOUS ROCKS REGIONAL GEOLOGIC SETTING Texas, University of Texas at Austin M.S. thesis, 55 p. [Igneous rocks of the Cornudas Mountains have been described by Clabaugh (1941), Zapp (1941), Timm (1941), (4.5 m) thick and are present only on northwest side of Chattfield Mountain; these rocks are The intrusive bodies that form the peaks of the Cornudas Mountains represent a part of the north-northwest- Woodward, L.A., Callender, J.F., Gries, J., Seager, W.R., Chapin, C.E., Zilinski, R.E., and Schaffer, Figure 1. Index map showing regional physiographic setting of the Cornudas The Cornudas Mountains are in the easternmost part of the Basin and Range province of southern New DESCRIPTION OF MAP UNITS Barker and others (1977), Barker and Hodges (1977), McLemore and Guilinger (1993), McLemore and others similar to those described by Kues and Lucas (1993) as the Campagrande Formation on south- trending mid-Tertiary calc-alkaline to alkaline Trans-Pecos magmatic belt of western Texas and New Mexico (Mc- W.L., 1975, Tectonic map of the Rio Grande region, Colorado–New Mexico border to Presidio, Mountains (map area shown in pink), south-central New Mexico and adjacent Texas. Mexico. The area is located near the center of the Otero-Diablo platform, which separates areas of Tertiary and (1996), and Schreiner (1994). The following descriptions are taken from their work. K-Ar age determinations east flank of Chattfield Mountain. The Cox Sandstone overlies the Campagrande at Chattfield Lemore and others, 1996). The predominantly alkaline intrusive rocks of the Cornudas Mountains give way to Texas, in Seager, W.R., Clemons, R.E., and Callender, J.F., eds., Las Cruces Country: New Mex- SURFICIAL DEPOSITS Quaternary faulting of the Rio Grande rift on the west from the Salt Basin graben and the adjacent Guadalupe reported below are from Barker and others (1977)] Mountain, and elsewhere rests unconformably on the Permian San Andres Formation (Psa). calc-alkaline intrusions of the Hueco Mountains, about 30 mi (50 km) to the west (fig. 1). The composition of the ico Geological Society Guidebook 26, p. 239. The Cox Sandstone consists of a basal, rounded to angular chert-pebble conglomerate overlain Mountains on the east (fig. 1). The Cornudas Mountains are underlain by Permian limestone and dolomite, Creta-
Qa Stream floodplain alluvium (Holocene)—Sand, silt, and clay deposited in (1) broad, open stream alkaline intrusive rocks of the Cornudas Mountains is predominantly syenite and phonolite. The most mafic rock Zapp, A.D., 1941, Geology of the northeastern Cornudas Mountains, New Mexico: Austin, Texas, Nepheline syenite (Oligocene)—Medium- to light-gray, mostly coarse-grained, equigranular to ceous sandstone and shale, and late Eocene to early Oligocene alkaline intrusive rocks. The intrusive rocks are valleys, (2) confined ephemeral stream channels, and (3) areas where drainage is partly blocked Tns by interbedded silty to sandy, light-gray, thin-bedded limestone and orange-tan to reddish- is the poorly exposed nepheline-bearing augite syenite (Tas) of the Chess Draw area; the most felsic rock, quartz- University of Texas at Austin M.S. thesis, 63 p. by man-made earthen dams. Where exposed, consists of upper zone of 1.5- to 2-ft- (0.45–0.6 slightly porphyritic nepheline syenite. Consists of anorthoclase, nepheline, clinopyroxene, brown to cream-white, calcareous, quartz-rich, crossbedded sandstone; locally, channel-fill part of the Tertiary Trans-Pecos magmatic belt (Barker and others, 1977) and form the major peaks of the Cornu- bearing syenite (Tqs), underlies Cornudas Mountain (Barker and others, 1977). The intrusive bodies vary consid- Tns1 Tns2 m) thick, tan-brown, clay-and silt-rich sand enclosing isolated pebbles; a medial zone of 1-ft- anhedral fayalite mantled by red hornblende, and minor to trace amounts of biotite, apatite, zir- deposits of lithic pebble conglomerate are interlayered with sandstone. Maximum thickness of das Mountains, which are, from east to west, Black, Cornudas, Wind, Chattfield, San Antonio, and Deer Moun- erably in their shape and form, as discussed below. Flow foliation is common in all intrusive rocks and particularly thick (0.3 m) silty sand interlayered with yellow-white 2- to 4-in.-thick (5.1–10.2 cm) layers of con, and muscovite. Exposures on Wind and Deer Mountains range from weakly to strongly the Cox is about 100 ft (30.5 m) tains, Flat Top, and Alamo Mountain. The Cornudas Mountains lie above the faulted, western edge of the buried well developed near contacts with adjacent sedimentary rocks. Intrusive bodies range from sills where foliation is

calcium carbonate-cemented sand, silt, and clay; and a lower zone of unknown thickness of foliated. Wind Mountain units subdivided into medium grained (Tns2) and coarse grained Km Metamorphosed calc-silicate rock (Lower Cretaceous)—Yellow-white to pale-green, fine-grained Pennsylvanian Pedernal uplift; alkaline rocks apparently intruded along the pre-Permian faults and invaded Paleo- subparallel to the enclosing, nearly flat-lying sedimentary rocks (Flat Top, and Black, San Antonio, and Chattfield clay, silt, and sand enclosing clasts ranging in size from pebbles to small boulders. Maximum (Tns1) after McLemore and others (1996); medium-grained units are most suitable for industrial metamorphosed calcareous rock that rests directly on Alamo Mountain sill. Less than 5 ft (1.5 zoic sedimentary rocks lying unconformably on the uplifted Precambrian basement (Black, 1975). Mountains), to plug-like bodies where foliation is steep (Deer and Wind Mountains), to irregularly shaped intrusive exposed thickness about 10 ft (3 m) use. K-Ar age of biotite from Deer Mountain is 31.6 Ma m) thick complexes with variable foliation where the level of erosion has exposed both feeder bodies and off-shooting sills   SEDIMENTARY ROCKS (Cornudas and Alamo Mountains). Magnetic data (Nutt and others, 1997) indicate a major, buried intrusive body Permian sedimentary strata, the oldest exposed rocks in the study area, make up gently rolling hill and plain northwest of Wind Mountain and in the Chess Draw area at a depth of about 2,200 ft (660 m). topography of this part of the Otero-Diablo platform. Three mappable Permian formations are exposed in the Contacts between intrusive and sedimentary rock are surprisingly sharp, and the lack of anything more than Cornudas Mountains. From oldest to youngest, they are: dark-gray, cherty limestone [Hueco Formation (Ph)]; irregular and local metamorphism and alteration is striking. The Chess Draw area in the central part of the map generally poorly exposed gypsum, shale, and limestone [Yeso Formation (Py)]; and dolomite, dolomitic limestone, area is the one small area of altered rock that has been prospected for metallic mineral resources. limestone, and minor clastic rocks [San Andres Formation (Psa)]. Only the Yeso Formation, about 100 ft (30.5m) Any use of trade names in this publication is for GEOLOGIC MAP OF THE CORNUDAS MOUNTAINS, OTERO COUNTY, NEW MEXICO thick, is completely exposed in the map area. The base of the Hueco Formation is not exposed, and the upper SYN-INTRUSIVE STRUCTURES descriptive purposes only and does not imply part of the San Andres was removed by erosion prior to deposition of the overlying Cretaceous strata. Folds endorsement by the U.S. Geological Survey On the New Mexico State geologic map (Anderson, 1994), only two formations are shown in the Cornudas By Rocks that underlie the Otero platform are deformed by gentle folds and minor faults (Black, 1975; Wood- area: the gypsiferous Yeso Formation and the overlying San Andres Formation. On the Geologic Atlas of Texas For sale by U.S. Geological Survey Information Services map of the Van Horn–El Paso area directly south of the map area (Barnes, 1975), three Permian formations are ward and others, 1975). The relatively undeformed character of the platform rocks changes dramatically in the Box 25286, Federal Center, Denver, CO 80225 J. Michael O’Neill and Constance J. Nutt mapped in the southernmost Cornudas Mountains: the lowermost Hueco Formation, the Permian Victorio Peak vicinity of the Cornudas Mountains, where a complex series of gently to steeply dipping, locally asymmetric folds 1998 Formation, and the Permian undifferentiated Leonardian limestones. The Victorio Peak overlies the Hueco on the appear to be related to intrusion of the igneous rocks. Elongate domes or anticlines are centered on Cornudas This map is also available as a PDF at http://greenwood.cr.usgs.gov