Geologic Map of the Tularosa Mountains 30′ Z 60′ Quadrangle, Catron County, New Mexico

Compiled by James C. Ratté

Prepared in cooperation with the New Mexico Bureau of Mines and Mineral Resources, a division of the New Mexico Institute of Mining and Technology

Pamphlet to accompany GEOLOGIC INVESTIGATIONS SERIES I–2619

2001

U.S. Department of the Interior U.S. Geological Survey Contents

Discussion 1 Introduction 1 Stratigraphy and Correlation of Map Units 1 Datil Group (35–32 Ma) 1 Mogollon Group (32–28 Ma) 1 Spears Group (Eocene to Miocene) 2 Gila and Santa Fe Groups (Miocene to Pleistocene) 2 Structure 2 Mineral Deposits 3 Description of Map Units 3 Surficial Deposits 3 Volcanic and Volcaniclastic Rocks 3 Older Sedimentary Rocks 10 References Cited 11 DISCUSSION Datil Group (35–32 Ma)

Datil Group volcanic rocks in the Tularosa Moun­ INTRODUCTION tains quadrangle are represented by multiple, thin ignim­ The Tularosa Mountains 30' Z 60' quadrangle is in brite outflow sheets and a much greater volume of southwestern New Mexico just east of the Arizona state andesitic lava flows. The ignimbrites occur mainly in scat­ line (fig. 1). U.S. Highway 180 provides access along the tered outcrops around the margins of the Plains of San western side of the quadrangle, and New Mexico Highway Agustin in the northeastern part of the quadrangle, where 12, which enters the quadrangle in its northeastern corner, they commonly are separated by a few meters of volcani­ joins U.S. Highway 180 near Reserve, the seat of Catron clastic sedimentary rocks. Individual tuff units range from County and the largest community in the quadrangle (fig. about 0 to 30 m thick. In the western part of the quadran­ 2). U.S. Highway 180, New Mexico Highway 12, and part gle, the ignimbrites are thinner (0–2 m thick), are largely of New Mexico Highway 32 are the only paved highways uncorrelated, and consist chiefly of discontinuous layers in in the quadrangle, but most parts of the area can be the upper Pueblo Creek Formation, above the andesite of reached from National Forest gravel roads and trails. Other Dry Leggett Canyon. settlements include Luna, along U.S. Highway 180, and Andesitic lava flows of Dry Leggett Canyon (unit Apache Creek, Aragon, and Old Horse Springs, along New Tla) are the only non-ignimbrite units in the Datil Group Mexico Highway 12. in the quadrangle. They have an aggregate thickness of as The Continental Divide (fig. 2) enters the Tularosa much as 300 m and cover large areas of the western part of Mountains quadrangle about midway along its northern the quadrangle, north and west of the San Francisco Moun­ border and continues irregularly southward to within about tains fault zone (fig. 4). 6 km of the southern border, where it turns eastward and The dacitic to rhyolitic Datil Group ignimbrites rep­ leaves the quadrangle a little south of center of the eastern resent the thin, distal, outflow sheets of regional ash-flow border (fig. 2). Streams in most of the east half of the tuffs, although only two of the eight ignimbrites that have quadrangle, north of the Continental Divide, drain into the been mapped in this quadrangle have known sources. The closed San Agustin basin. West of the Continental Divide, 32-Ma Hells Mesa Tuff (unit Thmt) is from the Socorro streams drain mainly westward to the San Francisco River, caldera, east of the Tularosa Mountains quadrangle a major tributary of the Gila River, and south of the Conti­ (Osburn and Chapin, 1983), and the 34.9-Ma Kneeling nental Divide streams drain into the Middle and East Forks Nun Tuff (unit Tkt) is from the Emory caldera in the Black of the Gila River. Range, to the south (Elston and others, 1975). The The Tularosa 30' Z 60' quadrangle is covered by 31.6-Ma Caballo Blanco Tuff (unit Tcbt) probably was thirty-two 7a-minute topographic quadrangles, and all but erupted from an unidentified source cauldron near the three of the quadrangles have been geologically mapped at a southern end of the Black Range, west of Truth or Conse­ scale of 1:24,000 by the U.S. Geological Survey (fig. 2). In quences (fig. 1). The source(s) for the other Datil Group addition, a number of older, mainly reconnaissance, geologic ignimbrites are most likely buried beneath the Plains of maps from other sources have been used in this compilation San Agustin. A proposed genetic relationship between the and these are shown in figure 3. Horse Springs dacite (unit Thsd) and the Blue Canyon The Tularosa Mountains quadrangle is bordered on Tuff (Tbct) (Ratté, Modreski, and others, 1994, p. 198) is the north by the Quemado 30' Z 60' quadrangle, which was possible evidence for a buried Blue Canyon Tuff caldera mapped by Chamberlin and others (1994), and on the south beneath the plains. This is an alternative to the proposed by the Mogollon Mountains 30' Z 60' quadrangle, which is Crosby Mountains caldera, or volcano-tectonic depression, covered by geologic maps at various scales, but mainly by of Bornhorst (1976) and Elston (1984, 1989). The evidence a reconnaissance geologic map of the Gila Wilderness aganist a Crosby Mountains caldera was summarized by (Ratté and Gaskill, 1975). Chamberlin (1994, p. 16-18).

Mogollon Group (32–28 Ma) STRATIGRAPHY AND CORRELATION OF MAP UNITS The Mogollon Group volcanic rocks comprise all of With the exception of a small, isolated fault block of the ignimbrites and associated lava flows that are younger Permian strata on the northern edge of the Plains of San than Caballo Blanco Tuff but older than the volcaniclastic Agustin, the rocks in the Tularosa Mountains quadrangle are Gila Group and its interlayered rhyolitic to basaltic rocks entirely Eocene to Quaternary volcanic rocks, with interlay­ (Cather and others, 1994). Ignimbrites of the Mogollon ered volcaniclastic sedimentary rocks, and Quaternary surfi­ Group in the Tularosa Mountains quadrangle are mainly cial deposits. The Tertiary volcanic rocks comprise the Datil outflow facies of regional tuffs (as opposed to intracaldera and Mogollon Groups (Cather and others, 1994), and the vol­ facies) and include La Jencia Tuff (unit Tlt), from the caniclastic sedimentary rocks are separated into the Spears Magdalena-Sawmill caldera west of Socorro; Vicks Peak Group, and the Gila and equivalent Santa Fe Groups. The Tuff (unit Tvt), from the Nogal Canyon caldera at the Gila Group has a number of intercalated basaltic lava flows southern end of the San Mateo Mountains, southwest of and andesitic to rhyolitic eruptive centers. Socorro; and Davis Canyon Tuff (unit Tdt), Shelley Peak

1 Tuff (unit Tst), Bloodgood Canyon Tuff (unit Tbt), and Volcanic rocks that are interlayered with the volcani­ Tuff of Triangle C Ranch (unit Tct), all from the Bursum clastic rocks are commonly associated with specific volca­ caldera complex in the Mogollon Mountains to the south. noes or volcanic centers. They range from andesites and These tuffs range between 29.0 Ma (Davis Canyon) and rhyolites of middle Miocene age, to predominantly basal- 28.0 Ma (Bloodgood Canyon and Triangle C Ranch). tic, small-volume lava flows and cinder cones of Miocene Lava flows, ranging from andesite and basalt to rhyo­ to Pleistocene age. lite, make up the greater volume of the volcanic rocks of the Mogollon Group in the Tularosa Mountains quadran­ STRUCTURE gle. They occur throughout the Mogollon Group, whereas lava flows in the Datil Group are confined to its central The pattern of dominant northeast-trending and subor­ part. Major lava flows in the Mogollon Group comprise the dinate northwest, east-west, and northerly trending normal andesitic Telephone Canyon volcano; the high-silica Tay­ faults (fig. 4) represents the prevalence of regional exten­ lor Creek Rhyolite dome field; the rhyolites of Gwynn sional forces in the Tularosa Mountains quadrangle during Canyon, Bat Cave Wells, Stallings Tank, and Hay Canyon; Neogene time. Although horizontal to moderately plunging the Squirrel Springs Canyon Andesite; and the several slickensides are present on some faults in the San Francisco Bearwallow Mountain Andesite volcanoes that are alined Mountains fault zone, they are rare and weak, and they prob­ along the southeast side of the Plains of San Agustin and ably represent only minor strike-slip and oblique movement elsewhere. on these predominantly dip-slip, normal faults. Consistent with this extensional structural setting are the several volca­ nic centers along or adjacent to the major fault systems. Spears Group (Eocene to Miocene) The fault patterns in this quadrangle further define a number of complex, en echelon grabens and half-grabens, The Spears Group (Cather and others, 1994) includes including the Reserve, Luna, Sand Flats, and San Augustin all of the epiclastic and other volcaniclastic rocks that are grabens (fig. 4). The Reserve half-graben (Crews, 1990, interlayered with the volcanic rocks of the Datil and Mog­ 1994), which typifies the development of extensional struc­ ollon Groups and that overlie the Eocene Baca Formation tures in this area, is filled with Gila Group basin-fill of in the Quemado 30' Z 60' quadrangle (fig.1) and else- Miocene to Pleistocene(?) age. The San Agustin graben, on where. Lower, middle, and upper Spears Group, and con­ the other hand, is still an aggrading, closed basin, with fill of stituent formations, were defined and mapped in the Pliocene(?) and Pleistocene age (Markgraf and others, 1984), Quemado quadrangle (Chamberlin and others, 1994) but but there is no evidence of current subsidence of the graben. have not been carried south yet into the Tularosa Moun­ The buried northern margin of the 28-Ma Bursum tains quadrangle. Here the Spears Group is divided into caldera of the Mogollon Mountains caldera complex is Tsl Tsu lower and upper units (units and ) where the sedi­ interpreted to be near the central southern border of the mentary units are below or above the andesite of Dry Leg­ quadrangle, where it is identified by the juxtaposition of gett Canyon, respectively. The lower Spears is locally phenocryst-poor, post-caldera rhyolite lava flows inside the called Pueblo Creek Formation, which is subdivided caldera and presumed pre-caldera, older, phenocryst-rich, locally into upper and lower Pueblo Creek Formation, coarsely porphyritic rhyolite flows on Elk Mountain (28 where it is above or below Andesite of Dry Leggett Can- Ma, Taylor Creek–type) in the caldera wall. Confirmation yon ( Ratté, 1989). of the relative ages of the two rhyolites is pending the In the southwestern part of the Tularosa Mountains results of 40Ar/39Ar dating. The “New Mexico Geologic quadrangle, the volcaniclastic rocks of the Spears Group Highway Map” (New Mexico Geological Society, 1982) grade into mudflows and lahars that contain an increasingly also shows the northern margin of the Bursum caldera in greater component of lava flows, eventually attaining the this area, but older rhyolite is shown inside the caldera and characteristics of vent facies volcanic rocks rather than younger rhyolite in the wall, and thus the geologic units volcaniclastic sedimentary rocks. Thus, the Spears Group are incompatible with the interpretation presented here. nomenclature of Cather and others (1994) is probably best Smith and Rhodes (1974) proposed a buried caul­ restricted to the northwestern part of the Mogollon-Datil vol­ dron at the southwest end of the San Agustin graben, canic field, where fluvial processes clearly predominate over which they called the Squirrel Springs volcano-tectonic volcanic processes in the origin of the volcaniclastic rocks. depression, and attributed its collapse to eruption of their Tularosa Canyon Tuff. They cited a shallow structural Gila and Santa Fe Groups (Miocene to Pleistocene) basin in which the Bearwallow Mountain Andesite presum­ ably ponded and an arcuate pattern of ring faults as the evi­ The Gila and Santa Fe Groups are equivalent names dence for this buried cauldron. Because the 25- to 26-Ma for the volcaniclastic sedimentary rocks and interlayered Bearwallow Mountain is much younger than the 31-Ma volcanic rocks that were deposited during the culminating Tularosa Canyon Tuff, and the arcuate faults cut only and waning stages of regional extension (basin and range younger rocks, they proposed that the original ring faults tectonism) in the Mogollon-Datil region. These rocks are were rejuvenated both before and after the Bearwallow included in the Gila Group if they occur west and south of ponded in the rejuvenated collapse. the Continental Divide and in the Santa Fe Group if they Although the John Kerr Peak and Squirrel Springs occur east and north of the divide. Canyon 7a-minute quadrangles are two of the three that were

2 not remapped in this study (figs. 2 and 3), reconnaissance for Deposits of prehistoric lake San Agustin (B.B. this compilation failed to provide evidence to support the Houser in Ratté and others, 1990) presence of a structural basin beneath Bearwallow Mountain Qsb Bar and barrier ridge deposits (Holocene Andesite in this area, or a buried caldera. The supposed thick­ and Pleistocene)—Variously oriented lenses ening of the Bearwallow due to ponding in a structural basin of sand, pebbles, and cobbles deposited by by rejuvenation of ring fractures is probably better explained by constructional accumulation of flows around vents and longshore currents and wave action; gener­ variable erosion of this and other Bearwallow accumulations. ally 50–100 m wide and less than 3 m high The proposed arcuate ring faults are based on faults that can Qsfd Fan delta deposits (Holocene and Pleis­ be shown only to have had post-Bearwallow movement, and tocene)—Vegetated, fan-shaped deposits of the arcuate traces are themselves largely buried beneath allu­ undetermined composition beneath modern vium and thus may be artifacts of geological speculation. alluvium at mouths of some streams along 40 39 Furthermore, new Ar/ Ar ages of 31.7 Ma for the Tularosa shoreline of prehistoric lake San Agustin Canyon Tuff (Smith and Rhodes, 1974) (which should be Qss Shoreline deposits (Holocene and Pleis­ abandoned) shows that it correlates as a thin, distal outflow of tocene)—Chiefly sand, gravel, and silt the Caballo Blanco Tuff, which has a center of distribution and probable source far to the south or southeast in the Mog­ deposited along shore of prehistoric lake San ollon Mountains, Pinos Altos Range, or Black Range, near Agustin Silver City ( McIntosh and others, 1992, p. 864). Qac Colluvium and alluvium (Holocene and Pleis­ tocene)—Mainly older alluvium in fan MINERAL DEPOSITS deposits that commonly grade into slope wash and talus. May include younger allu­ There are no known viable mineral resources in the vium, unit Qa, and alluvial terrace gravels quadrangle, except sand and gravel, but there has been Ql Landslide deposits (Holocene and Pleis­ extensive exploration for oil and gas in Paleozoic sedimen­ tocene)—Include semicoherent blocks con­ tary rocks beneath the volcanic cover rocks. The SWEPI sisting of rocks in stratigraphic sequence as No. 1 oil test well is located in sec. 2, T. 4 S., R. 13 W., in well as slumped masses of mixed litholo­ the northeastern part of the Horse Mountain West quadran­ gies. Some slide blocks within extensive gle, west of Horse Mountain. landslide slopes are identified by their own The presence of silicic and altered intrusions at the surface and in the subsurface along the extensional struc­ lithologic map unit symbols, as at southwest tures of the Morenci Lineament indicates the possibility of end of Plains of San Agustin, northeast of hydrothermal mineral deposits in Paleozoic and other sedi­ John Kerr Peak mentary or volcanic rocks along this structural zone. The Qp Piedmont slope deposits (Pleistocene)—Chiefly most highly mineralized rocks found in the quadrangle have boulders, sand, and gravel deposits on gently been the jasperoid-related iron- and zinc-rich jasperoid nod­ sloping erosion surfaces ules associated with quartz monzonite inclusions at the Cerro Caballo dome, or cone, near Old Horse Springs, vol­ canic center 2, figure 4 (Ratté, Modreski, and others, 1994). VOLCANIC AND VOLCANICLASTIC ROCKS

Volcaniclastic rocks of the Gila Group— DESCRIPTION OF MAP UNITS Basin-fill deposits eroded from uplifted blocks during extensional breakup of [Isotopic ages followed by an asterisk (34.7 Ma*) are Mogollon-Datil volcanic field to form 40Ar/39Ar ages; all others are conventional K-Ar ages] incipient basin-and-range topography QTg Gila Group, undivided (Pleistocene(?) to SURFICIAL DEPOSITS early Miocene)—Nonindurated to well- indurated clastic sedimentary rocks, which Qa Alluvium (Holocene)—Mainly boulders, gravel, are readily subdivided only where interlay­ sand, and silt in channels and on floodplains ered with lava flows and tuffs from nearby of major perennial and intermittent streams volcanic eruptive centers. Locally includes Qsa Playa alluvium of the Plains of San Agustin beds of basaltic cinders, as along San Fran­ (Holocene)—Modern playa sediments of cisco River in O Block Canyon quadrangle. gray, silty clay containing minor sand-sized Volcanic clasts are predominantly derived calcite grains. Alluvium is underlain by at least from local sources 610 m of lacustrine silt, clay, and alluvial grav­ QTgu Upper Gila Group (Pleistocene(?) to middle els of Holocene to Pliocene(?) age as deter- Miocene)—Nonindurated to poorly indu­ mined in a drill hole in southern part of plains rated, bouldery, volcaniclastic sand and gravel

3 mapped above lava flows of Eagle Peak Tfb Basalt on Flat Top Mesa (Ratté, Bove, and volcano McIntosh, 1994) (Miocene, 9 Ma*)— QTgl Lower Gila Group (middle to early Fine-grained lava flows containing 1- to Miocene)—Chiefly well-indurated, coarse- 3-mm-long clinopyroxene phenocrysts and grained, volcaniclastic beds containing quartz xenocrysts having pyroxene reaction clasts of locally derived volcanic rocks; rims; along Negrito Creek, southwest of beneath Eagle Peak lava flows and above Eagle Peak Bearwallow Mountain Andesite or older Rocks of Apache Peak volcano—Intru­ rocks sive-extrusive, andesite dome complex at an QTs Volcaniclastic rocks of the Santa Fe Group eruptive center along southeastern margin of (Pleistocene to Miocene)—Volcaniclastic Morenci-Reserve fault zone in O Block Can- rocks north and east of the Continental yon 7a-minute quadrangle Divide are arbitrarily distinguished from Taa Andesite at Apache Peak (Miocene, 10.6 the Gila Group south and west of the Ma, H.H. Mehnert, oral commun., divide. Santa Fe Group mapped only at 1990)—Fine-grained, seriate-porphyritic to head of Shaw Canyon, at east edge of granular, two-pyroxene, plagioclase flows, quadrangle flow breccia, lahars, and possible intrusive Volcanic rocks interlayered with the Gila facies Group—Includes thin, tholeiitic and Rocks of Eagle Peak volcano—Multiple erup­ alkali-olivine basalt flows, distinct from tive centers comprising a composite dome of older Bearwallow Mountain Andesite volca­ andesite and dacite flows around an eccentric, noes. Also includes andesitic, dacitic, and dacite plug dome at Eagle Peak (Bove and rhyolitic volcanoes localized along north- others, 1995) east-trending Morenci-Reserve fault zone Tedp Central dacite plug (Miocene, 11.4 (Ratté, 1989), or Morenci lineament (Chapin Ma*)—Dacite agglomerate apron, about 0.8 and others, 1978) km in diameter, intruded by porphyritic dac­ QTb Basalt (Pleistocene and Pliocene, 0.9–2.5 ite plug, about 0.5 km in diameter; plug con­ Ma)—Includes alkali-olivine basalt and tains about 2.3 percent small plagioclase tholeiitic basalt flows at Luna, Spur Lake phenocrysts, traces of orthopyroxene and cli­ Basin, Apache Creek, Feathery Hill, and else- nopyroxene and rare hornblende where. May have diktytaxitic texture Tedu Upper dacite flows (Miocene)—Anhydrous QTd Basalt dikes (Pleistocene and Pliocene)— dacite containing about 2.5 percent small Dikes associated mainly with cinder cones in phenocrysts, mostly plagioclase and minor northwestern part of quadrangle orthopyroxene QTbc Basalt scoria (Pleistocene and Pliocene)— Tedl Lower andesite and dacite flows (Miocene, Cinders and bombs in cinder cones and 12 Ma*)—Hydrous andesite and dacite con­ around vents taining about 9 percent phenocrysts, mainly Tb Basalt, andesite, and dacite, undivided plagioclase and minor orthopyroxene, horn­ (Miocene)—Basalt flows commonly charac­ blende, and biotite, and rare clinopyroxene terized by large (0.5–3 cm) plagioclase Tedw Wilson Canyon andesite flows (Mio­ (labradorite) and pyroxene (augite) pheno­ cene)—Anhydrous andesite related to pro- crysts; some flows contain granitic crustal posed Wilson Canyon satellitic eruptive cen­ xenoliths and quartz xenocrysts ter, containing about 8 percent phenocrysts Tbd Basalt dikes (Miocene)—Generally short, thin and glomerocrysts, mainly plagioclase, minor dikes 1–3 m wide and a few meters to a few orthopyroxene, and a trace of clinopyroxene. tens of meters long; commonly resemble Also present are hornblende-bearing enclaves Miocene basalt flows, units Tb and Tsb, by of finely porphyritic, hydrous andesite that having large pyroxene and plagioclase phe­ indicate possible magma mixing nocrysts. Mapped mainly in southwestern Tedm Milligan Mountain andesite-dacite flows part of quadrangle (Miocene, 12 Ma*)—Hydrous, borderline Tbcc Basaltic scoria, cinders, and bombs andesite-dacite related to Milligan Mountain (Miocene)—Generally red, scoriaceous flows satellitic eruptive center; flows contain about and pyroclastic deposits associated mainly 12 percent phenocrysts and glomerocrysts, with basalt lava flows in south-western corner mainly plagioclase and minor hornblende and of quadrangle, along San Francisco River orthopyroxene, and traces of clinopyroxene

4 Ted Andesite dike at Dry Mesa (Miocene)— Extends over elongate area northwest of Fine-grained dike that is petrographically sim­ central plug, unit Thp ilar to Milligan Mountain flows and contains Tha Megacrystic andesite lava flow (Miocene, sparse plagioclase, hornblende, and orthopy­ 12 Ma*)—Andesite-trachyandesite contain­ roxene microphenocrysts, indicating that it ing abundant megacrysts of anorthoclase and might havebeen a feeder for Millgan Mountain (or) sanidine and 0.5- to 1-cm augite pheno­ flows formerly present on Dry Mesa crysts. Single flow, a few tens of meters thick, Rocks of Horse Mountain volcano—Com­ has highly oxidized, red spatter locally at posite rhyodacitic dome and flows along base. Occurs only in ledge about 1 km long in northwest side of San Agustin graben, in lower slopes near northeast corner of Horse northeast corner of quadrangle (Ratté and Mountain and as a small landslide or fault others, 1990) block north of New Mexico Highway 12 in Thv Predominantly dacitic, rhyolitic to andes­ the same area itic lava flows (Ratté and others, 1990) Tsb Basalt of Saliz Hill (Ratté, 1980) (Miocene, (Miocene, 12–14 Ma*)—Wide range of 12.2 Ma)—Fine-grained, commonly flow- fine-grained and finely porphyritic platy and layered basalt or basaltic-andesite near south- flow-banded, red to black and gray lavas and west corner of quadrangle flow breccias Tkb Basalt at Kiehnes Canyon (Ratté, Bove, and Thd Northwest-trending, andesitic-dacitic McIntosh, 1994) (Miocene, 13.5 Ma*)— breccia dikes (Miocene)—Dikes that Small plug, about 100 m in diameter, sur­ intrude, and maybe feed, Horse Mountain rounded by scoriaceous, red cinders and vent or flow breccia northwest of main erup­ bombs. Two associated basalt flows, each less tive center than 10 m thick; basalt ranges from Tht Pyroclastic rocks (Miocene)—Rare bedded fine-grained to seriate porphyritic and con­ outcrops beneath eastern edge of Horse tains phenocrysts of plagioclase, pyroxene, Mountain lava flows; probably from precur­ and olivine altered partly to iddingsite. sor explosive eruptions of Horse Mountain Restricted to Kiehnes Canyon area southwest volcano. Tuffs contain plagioclase, biotite, of Eagle Peak and hornblende, and are mixed with surge and Rocks of John Kerr Peak volcano—Complex other volcaniclastic deposits of dacite and rhyolite domes, flows and Thp Dacite plug (Miocene)—Very fine grained breccia surrounded by Bearwallow Moun­ porphyritic rocks containing sparse pheno­ tain Andesite at northeast end of Tularosa crysts and microphenocrysts of plagioclase, Mountains clinopyroxene and orthopyroxene, biotite, Tjr Rhyolite domes and flows (Smith, 1976) and hornblende. Light and dark-gray phases (Miocene, ≈13 Ma, Marvin and others, are petrographically similar but have sharp 1987)—John Kerr Peak quartz-latite of Smith contacts, which may be partly the result of (1976). Coarsely porphyritic rhyolite and color changes and related more to hydrother­ rhyodacite contains phenocrysts as much as 2 mal alteration than to differences in composi­ cm long, including various proportions of tion. Occupies northwest-elongate area near sanidine-mantled plagioclase, quartz, sani­ Horse Peak in central part of Horse Mountain dine, hornblende, biotite, and both clinopy­ volcano roxene and orthopyroxene Thdr Aplite dikes (Miocene)—Pink, 3- to 5-m Tmr Rhyolite near Maverick Peak (Ratté, 1989) thick, northwest-trending dikes adjacent to (Miocene, ≈14 Ma)—Present only along San southeast contact of central intrusive plug. Francisco Mountains fault zone, west of U.S. Dikes contain 30–40 percent 0.25- to 0.5-mm Highway 180. Includes small quartz-porphyry microphenocrysts and rare 1-mm phenocrysts rhyolite plug, about 0.7 km northeast of Mav­ of plagioclase, green amphibole, and biotite; erick Peak, and domal rhyolite flows or intru­ matrix is subvitreous and contains patches of sive rhyolite in hanging wall of San Francisco granophyre along cracks; resembles rock of Mountains fault zone central plug Tmrd Rhyolite dike in rhyolite near Maverick Thb Vent(?) breccia (Miocene)—Finely vesicu­ Peak (Miocene) lar, light- to dark-gray, very finely brecci­ Tli Porphyritic quartz-diorite intrusions at Wet ated, aphyric, generally glassy, structureless Leggett Spring (Ratté, 1989) (Miocene, body. Intrusive vent breccia or flow breccia. ≈15 Ma, Marvin and others, 1987)—Quartz

5 diorite containing about 25 percent pheno­ Volcanic rocks of the Mogollon Group (Cather crysts and xenocrysts(?), including pale-pink and others, 1994) (Miocene and quartz (having corroded margins and Oligocene)—Voluminous caldera-related, pyroxene rims), plagioclase hornblende, and dacitic and rhyolitic ignimbrites (ash-flow biotite. The intrusion at Wet Leggett Spring, tuffs) and equally voluminous andesitic to south of Leggett Peak, has abundant coarse high-silica rhyolite lavas comprise culminat­ and fine-grained, hornblende-rich, cog­ ing eruptive phase of Mogollon-Datil volcanic nate(?) inclusions. Along San Francisco fault field, which includes main pulse 3 of mid­ zone southwest of U.S. Highway 180 in Wet dle-Tertiary ignimbrite flare-up of McIntosh Leggett Canyon (in Bull Basin 7a-minute and others (1992) quadrangle) Tmgu Mogollon Group, undivided (Miocene and Volcaniclastic rocks of the Spears Group Oligocene)—Mapped only at southwest edge (Osburn and Chapin, 1983) (Oligocene of Plains of San Agustin (where Squirrel and Eocene) Springs Canyon Andesite, unit Tsa; Shelley Tsu Upper Spears Group (Oligocene)—Volcani­ Peak Tuff, unit Tst; and Bloodgood Canyon clastic sedimentary rocks above Davis Can- Tuff, unit Tbt, are repeated and jumbled in yon Tuff and interlayered between volcanic landslide slopes) and north of Wagontongue rocks of the Mogollon Group (Cather and Mountain in southwest corner of Tularosa others, 1994) Canyon 7a-minute quadrangle, where Mog­ Tsl Lower Spears Group, undivided (Oligocene ollon Group tuff outcrops are too small to and Eocene)—Volcaniclastic sedimentary subdivide rocks equivalent to Pueblo Creek Formation Tad Andesite dikes (Miocene and Oligocene)— (Ratté, 1989). Mapped only beneath Caballo Fine-grained to porphyritic dikes; some of Blanco Tuff at south end of Plains of San uncertain age and correlation, scattered Agustin throughout Tularosa Mountains quadrangle Tslw White sandstone sequence of lower Spears Bearwallow Mountain Andesite (Oligocene, Group (Eocene)—Upper subdivision of 25–26 Ma, Marvin and others, 1987)— lower Spears Group; mapped only northwest Predominantly calc-alkaline, andesitic lava of Spur Lake Basin fault zone in northwestern flows, but ranging from dacite to basalt; part of quadrangle erupted from numerous, low-profile shield Tslg Green to gray sandstone sequence of lower volcanoes lacking in appreciable pyroclastic Spears Group (Eocene)—Lower subdivi­ components sion of lower Spears Group; mapped only Tba Basaltic-andesite to dacite lava flows northwest of Spur Lake Basin fault zone in (Oligocene)—Typically aphanitic to fine- northwestern part of quadrangle grained porphyritic flows; commonly are Tpu Upper Pueblo Creek Formation (Oligocene spotted with tiny, rusty-orange, iddingsitic­ and Eocene)—Rocks ranging from andesitic altered olivine. Major eruptive centers have lahars and thin lava flows (vent facies) in distinctive compositions, such as Pelona southwest corner of quadrangle to predomi­ Mountain and O Bar O Mountain, which are nantly mudflows and volcaniclastic conglom­ predominantly hypersthene andesite. Quartz erates and sandstones (alluvial facies) xenocrysts are common in the flows at many elsewhere. Overlies andesite of Dry Leggett localities Canyon (unit Tla). Units Tt and Tt1–4 are dis­ Tbad Andesitic dike (Oligocene)—Associated continuous, thin (0 to about 5 m thick) Datil with scoriaceous cinder cone remnants on Group ignimbrites interlayered in upper southwest flank of Pelona Mountain. Some Pueblo Creek Formation dikes, mapped as unit Tad (undivided), Tpl Lower Pueblo Creek Formation (Eocene)— undoubtedly also are of Bearwallow Moun­ Volcaniclastic conglomerate and sandstone tain age, but their geologic relationships are containing highly rounded boulders and uncertain cobbles of Precambrian granitic rocks and Tbap Andesite plugs (Oligocene)—Fine-grained, fossiliferous Paleozoic limestone, as well as pervasively jointed, hypabyssal intrusive volcanic clasts. Underlies andesite of Dry rocks commonly marking major eruptive cen­ Leggett Canyon (unit Tla). Tuff of Bishop ters, as at Pelona Mountain and O Bar O Peak (unit Tpt) is interlayered near top of Mountain, and minor eruptive centers lower Pueblo Creek Formation elsewhere

6 Tbac Andesitic cinder and scoria deposits (Oli­ abundant oligoclase and biotite, and minor gocene)—Shown only as remnants of a small distinctive green clinopyroxene phenocrysts. cinder cone east of Coyote Peak between O Constitutes proximal to distal outflow sheet in Bar O Mountain and Pelona Mountain Tularosa Mountains quadrangle; derived from Thr Rhyolite of Hay Canyon (Oligocene?)— caldera complex in Mogollon Mountains, Light-gray, phenocryst-poor, high-silica rhy­ south of Tularosa Mountains quadrangle. May olite that covers buried northern margin of be mapped with Bloodgood Canyon Tuff Bursum caldera; has sparse, tiny, needle-like where too thin to show separately, as in Ful­ amphibole crystals. Underlain by rhyolite of lerton and Luna 7a-minute quadrangles Gwynn Canyon and overlain by Bearwallow Taylor Creek Rhyolite and associated Mountain Andesite rocks—Taylor Creek Rhyolite here includes Tfr Rhyolite at Frying Pan Creek (Oligo­ northwestern part of Taylor Creek Rhyolite cene?)—Small, phenocryst-poor rhyolite described by Duffield and Dalrymple (1990) intrusion between Frying Pan Canyon and San and similar or identical rhyolite domes and Francisco River in O Block Canyon flows to the north and west in Shaw Canyon, 7a-minute quadrangle. Intrudes Bloodgood the Collins Park area, and Elk Mountains, in Canyon Tuff and older rocks Tularosa Mountains quadrangle Tsr Rhyolite of Stallings Tank (Oligocene)— Tgt Tuff of Garcia Camp (Lawrence, 1985; Duf­ Rhyolite containing about 5 percent pheno­ field and Dalrymple, 1990) (Oligocene, 28.1 crysts, mainly oligoclase and minor biotite, Ma*, McIntosh and others, 1992)—Precur­ and traces of opaque oxide, clinopyroxene, sor, dome-related, rhyolitic pyroclastic flows apatite, zircon and anorthoclase(?). At head ranging from poorly indurated to weakly of Shaw Canyon, at east edge of Tularosa welded ignimbrite; average 20 percent phe­ Mountains quadrangle. Overlies Taylor nocrysts, mainly quartz and sanidine. Here Creek Rhyolite and Bloodgood Canyon Tuff includes local pyroclastic rocks associated in Shaw Canyon and underlies Bearwallow with rhyolite flows near head of La Jolla Can- Mountain Andesite yon, east of Collins Park (W.A. Duffield, oral Tct Tuff of Triangle C Ranch (Ratté and others, commun., 1994) 1990) (Oligocene, 28.1 Ma*, McIntosh and Ttr Taylor Creek Rhyolite (Duffield and Dal­ others, 1992)—Late high-silica rhyolite ig­ rymple, 1990) (Oligocene, 28.1 Ma*, McIn­ nimbrite from Bursum caldera. Commonly tosh and others, 1992)—Major rhyolite included as part of Bloodgood Canyon Tuff, dome complexes; high-silica rhyolite con­ with which it is virtually identical; locally taining moderate abundance of sanidine and mapped separately, as along Negrito Creek quartz phenocrysts, and minor plagioclase and east of O Bar O Mountain. Locally sepa­ and biotite. Wood tin nuggets from Taylor rated from Bloodgood Canyon Tuff by a meter Creek Rhyolite have been prospected in ped­ or two of pumiceous, volcaniclastic sandstone iment deposits and regolith near Whiskey Tbt Bloodgood Canyon Tuff (Elston, 1976) (Oli­ Canyon and Railroad Canyon, in Indian Peaks gocene, 28.1 Ma*, McIntosh and others, West 7a-minute quadrangle (Lawrence and 1992)—Phenocryst-rich, rhyolite ignimbrite Richter, 1986) outflow sheet from the Bursum caldera. Con­ Tsa Squirrel Springs Canyon Andesite (Rhodes tains abundant sanidine (moonstone) and and Smith, 1976) (Oligocene, 28.5 Ma*, quartz phenocrysts, rare biotite, and minor McIntosh and Chamberlin, 1994)—Gray tiny, distinctive yellow sphene crystals to reddish-gray, mainly very coarsely por­ Tca Basaltic-andesite of Cottonwood Canyon phyritic, plagioclase phyric andesite and (Oligocene)—Thin, discontinuous, reddish- basaltic andesite flows brown, fine-grained lava flow(s) locally Tvt Vicks Peak Tuff (Osburn and Chapin, 1983) present between Shelley Peak and Bloodgood (Oligocene, 28.6 Ma*, McIntosh and oth­ Canyon Tuffs along Cottonwood Canyon, ers, 1992)—Light-colored, phenocryst- poor near southeast corner of Plains of San Agustin ignimbrite outflow sheet derived from Vicks in Rail Canyon 7a-minute quadrangle Peak caldera in San Mateo Mountains, to east Tst Shelley Peak Tuff (Ratté and Gaskill, 1975) of Tularosa Mountains quadrangle. Com­ (Oligocene, 28.1 Ma*, McIntosh and oth­ bined with Davis Canyon Tuff (unit Tdt) ers, 1992)—Reddish-brown to light-gray, locally on north side of Eagle Peak, where too phenocryst-rich ignimbrite; contains thin to show both separately

7 Tgr Rhyolite of Gwynn Canyon (Oligocene, 28.7 northern margin of Bursum caldera, in Ma*, unpub. age, D.J. Bove, 1993)— south-central part of Tularosa Mountains Light-tan rhyolite containing abundant phe­ quadrangle nocrysts of quartz, sanidine, and biotite, and Tta Andesite of Telephone Canyon, undivided minor brown oxyhornblende and sphene. (Oligocene, 32.9–29.7 Ma*, D.J. Bove, Confined to vicinity of Gwynn Canyon unpub. ages, 1993)—Numerous andesite to along buried north margin of Bursum dacite and trachydacite flows and breccias; caldera, in Telephone Canyon 7a-minute mainly finely porphyritic and containing quadrangle small plagioclase, biotite, and hornblende Tlt La Jencia Tuff (Osburn and Chapin, 1983) phenocrysts (Oligocene, 28.9 Ma*, McIntosh and oth­ Volcanic rocks of the Datil Group (Osburn and ers, 1992)—Light-gray to reddish-brown, Chapin, 1983; Cather and others, 1994) phenocryst-poor, rhyolitic ignimbrite, which (Oligocene and Eocene)—Includes all of the crops out in Tularosa Mountains quadrangle regional ignimbrites and most of the andesitic only along southern edge of Plains of San to rhyolitic lavas erupted prior to the 31.4- to Agustin; represents distal outflow sheet from 29.0-Ma hiatus in major volcanic activity Sawmill Canyon–Magdalena caldera com­ defined by McIntosh and others (1991, 1992). plex near Socorro, east of Tularosa Mountains Exceptions in Tularosa Mountains quadran­ quadrangle gle are rhyolite flows of Bat Cave Wells and Tdt Davis Canyon Tuff (Ratté and Gaskill, 1975) Telephone Canyon volcano, both of which (Oligocene, 29.0 Ma*, McIntosh and oth­ may overlap boundary between Datil and ers, 1992)—Light-colored, phenocryst-poor, Mogollon Groups high-silica, rhyolite ignimbrite, which con­ Tdgu Datil Group, undivided (Oligocene and tains sparse tiny phenocrysts of quartz and Eocene)—Mapped only along south flank of sanidine. Tuff outflow sheet probably is Horse Mountain, where Datil Well, Kneeling derived from Mogollon Mountains caldera Nun, and Rock House Canyon Tuffs are jum­ complex south of the Tularosa Mountains bled in a slumped and faulted(?) sequence. quadrangle These outcrops are important in constraining Ta Andesite flows (Oligocene)—Thin, discontin­ distribution of rocks of Horse Mountain uous, fine-grained to porphyritic flows con­ volcano taining plagioclase and pyroxene phenocrysts. Tcbt Caballo Blanco Tuff (Elston, 1957) (Oli­ Interlayered with volcaniclastic rocks in upper gocene, 31.6 Ma*, McIntosh and others, Pueblo Creek Formation above andesite of 1992)—Light-colored, coarsely porphyritic, Dry Leggett Canyon, mainly north of Saddle rhyolitic ignimbrite. Contains abundant phe­ Mountain at west edge of Tularosa Mountains nocrysts of quartz, sanidine, oligoclase, and quadrangle and south of Monument Mountain biotite; minor opaque oxides, sphene, and in Dillon Mountain quadrangle oxyhornblende; and trace apatite, zircon, and Tbr Rhyolite of Bat Cave Wells (Ratté and others, clinopyroxene. Source of this distal ignim­ 1990) (Oligocene)—Gray to reddish-brown, brite outflow is unknown, but it is probably porphyritic rhyolite flows and domes, con­ from an occult caldera in Mogollon Moun­ taining about 5–15 percent phenocrysts, tains or southern Black range, or Twin Sisters mainly sanidine and (or) anorthoclase, minor cauldron complex, northwest of Silver City clinopyroxene and opaque oxide, and traces (McIntosh and others, 1992) of biotite, apatite, and zircon. Underlies Thmt Hells Mesa Tuff (Osburn and Chapin, 1983) Davis Canyon Tuff on south side Plains of (Oligocene, 32.1 Ma*, McIntosh and oth­ San Agustin and beneath Jack Peak, south of ers, 1992)—Light-colored, rhyolitic ignim­ Old Horse Springs, on north side of plains, brite containing abundant quartz, sanidine, where it was called rhyolite of Wye Hill by and plagioclase phenocrysts; minor opaque Bornhorst (1976). K-Ar ages range from 27.3 oxide and biotite; and traces of sphene, zir­ Ma to 32.2 Ma (Marvin and others, 1987, con, apatite, and hornblende. Thin, distal entries 121, 122, and 212) outflow sheet in Tularosa Mountains quad­ Rocks of Telephone Canyon volcano—Com­ rangle was derived from Socorro caldera to posite andesite domes at a complex eruptive east. Occurs only near head of South Fork center along South Fork, Negrito Creek. Alamocito Canyon and on east flank of Jack These are oldest rocks exposed along buried Peak, south of Old Horse Springs

8 Tt Distal outflow of regional ignimbrites (Oli­ map of Saliz Pass 7a-minute quadrangle gocene and Eocene)—Discontinuous, thin (Ratté, 1980) (0–5 m), partly reworked, tuffs. Correlations Tla Andesite of Dry Leggett Canyon (Ratté, uncertain; interlayered in upper part of 1989) (Eocene)—Widespread thick plagio­ Pueblo Creek Formation, lower Spears clase and pyroxene-phyric lava flows, which Group. Labeled Tt1–4, where present in occur between tuff of Bishop Peak (34.6 sequence. Tt3 (tuff of Luna) is tentatively cor­ Ma*) and andesites of Saddle Mountain vol­ related with Box Canyon Tuff by 40Ar/39Ar cano (about 33.3 Ma). Flows present mainly age of 33.62±0.1 Ma (McIntosh and others, northwest of San Francisco Mountains fault 1991, Appendix 1, p. 62) zone in northwestern part of quadrangle, and Rocks of Saddle Mountain volcano—Ande­ in adjoining Quemado 1:100,000 quadrangle site dome, or cone, and associated horn­ to the north blende-rich dikes at west edge of Bull Basin Tlai Possible plug or vent for andesite of Dry 7a-minute quadrangle (Ratté, 1989). At least Leggett Canyon (Eocene)—Isolated body half of Saddle Mountain volcano is in adjoin­ of columnar-jointed andesite about 300 m in ing Blue 15-minute quadrangle, New Mexico diameter, about 1 km north of Aragon; or may and Arizona be related to underlying topography Tas Andesite lava flows (earliest Oligocene or Rocks of Horse Springs volcano or volcanic latest Eocene, about 33.3 Ma)—Andesite center—Pyroclastic flows, block and ash flows containing 40–50 percent phenocrysts, flows, and lava flows(?) distributed about an mostly plagioclase, opaque oxide, and highly eruptive center or centers west of Old Horse oxidized mafic crystals, which include partly Springs to completely altered hornblende, and minor Thsd Horse Springs dacite (Ratté and others, clinopyroxene and orthopyroxene. Also con­ 1990; Ratté, Modreski, and others, 1994) tains minor cognate(?) inclusions having (Eocene, 33.7 Ma*, W.C. McIntosh, writ- hypautomorphic granular texture and miner­ ten commun., 1995)—Porphyritic dacite alogy similar to that of enclosing flows. containing abundant phenocrysts of oligo­ Flows crop out only near el. 2495 m in south- clase-andesine and biotite, minor opaque west corner of quadrangle on east flanks of oxides, green clinopyroxene, and trace zircon Saddle Mountain eruptive center, which lies and apatite. Block and ash flows, which con­ immediately to the west, in the Blue tain 2–3 m cognate quartz monzonite blocks 15-minute quadrangle and silicified and mineralized accidental Tasb Andesite agglomerate (Oligocene or lithic inclusions of Paleozoic rocks, probably Eocene)—Rounded clasts of hornblende- mark the main volcanic eruptive center. rich andesite breccia underlying lava flows Referred to elsewhere as “tuff breccia of around east side of Saddle Mountain eruptive Horse Springs Canyon” by Bornhorst (1976) center and Jones (1980), and as “pumice breccia of Tasd Andesite dikes (Oligocene or Eocene)— Old Horse Springs” by Ratté and Modreski Hornblende-rich dikes probably related to (1989, STOP 3–1, Pumice breccia of Old Saddle Mountain eruptive center; most are Horse Springs, p. 70–80) only a few meters to 10 m long, but one Thsb Megabreccia and mesobreccia (Eo­ north-south dike is about 5 km long cene)—Breccia consisting of slabs, tens of Tsca Andesitic intrusive-extrusive complex of meters long, of older Datil Group ignim­ Saliz Canyon (Eocene)—Fine-grained brites, and smaller breccia outcrops that andesite has microphenocrysts of plagioclase contain block-sized clasts of Squirrel and clinopyroxene and appears to intrude Springs Canyon Andesite and volcaniclas­ associated vent(?) breccia tic sedimentary rocks. Outcrops of Tscb Andesitic vent(?) breccia (Eocene, 33.6 Ma, megabreccia and mesobreccia, mostly too Marvin and others, 1987)—Breccia has small to be shown at this map scale, are abundant plagioclase, clinopyroxene and scattered along eastern margin of orthopyroxene, brown hornblende, and biotite north-south-trending belt of Horse Springs phenocrysts. K-Ar biotite age of 33.6±1.1 Ma dacite outcrops, possibly outlining margins indicates correlation with Eocene andesitic of a buried caldera source for Blue Canyon rocks rather than with a younger intrusive Tuff 6–8 mi in diameter (Ratté, Bove, and body, as interpreted previously on geologic others, 1994, p. 109–110) beneath alluvial

9 fans of Alamocito Creek reentrant, north of hornblende, apatite, and zircon. Scattered Plains of San Agustin outcrops north of Plains of San Agustin near Tbct Blue Canyon Tuff (Lopez and Bornhorst, Old Horse Springs and New Horse Springs and 1979; Osburn and Chapin, 1983) (Eocene, Horse Mountain are remnants of distal outflow 33.7 Ma*, McIntosh and others, 1992)— sheet from Emory caldera, in Black Range Gray, densely welded, dacitic ignimbrite con­ more than 100 km south and east of Plains of taining abundant phenocrysts of glassy sani­ San Agustin and Tularosa Mountains dine, dull-white plagioclase, minor biotite quadrangle and opaque oxide, and traces of green cli­ Tft Tuff of Farr Ranch (Ratté and others, 1990) nopyroxene, hornblende, zircon, apatite, and (Eocene, 35.6 Ma*, McIntosh and others, sphene. Petrographically, chemically, and 1992)—Light-gray to reddish-brown, phe­ texturally similar to younger Horse Springs nocryst-poor, rhyolitic ignimbrite. Sparse dacite. Unit may include Rock House Can- phenocrysts are mostly sanidine, but include yon Tuff locally minor plagioclase, biotite, clinopyroxene, Trt Rock House Canyon Tuff (Osburn and and opaque oxides, and accessory sphene, Chapin, 1983) (Eocene, 34.4 Ma*, McIn­ apatite, and zircon. Constitutes a thin, discon­ tosh and others, 1992)—Light-gray, phe­ tinuous outflow sheet that is petrographically nocryst-poor, rhyolite ignimbrite; source identical to Datil Well Tuff but commonly unknown. May be included locally with Blue separated from it by volcaniclastic sandstone. Canyon Tuff where outcrops are too small to Source unknown show separately Twt Datil Well Tuff (Lopez and Bornhorst, 1979) Tbrt Blue Canyon and Rock House Canyon Tuffs, (Eocene 35.5 Ma*, McIntosh and others, undivided (Eocene)—Mapped only where 1992)—Light-gray to light-pinkish-brown outcrops are too small to show tuffs sepa­ rhyolite ignimbrite containing moderate rately abundance of sanidine phenocrysts, minor Tlwt Tuff of Lebya Well (Ratté and others, 1990) clinopyroxene, plagioclase, biotite, and (Eocene, 34.7 Ma*, McIntosh and others, opaque oxides, accessory brown hornblende 1992)—Reddish-brown to purplish-gray, or allanite, zircon, and apatite, and rare densely welded rhyolite ignimbrite contain­ quartz. Thin, discontinuous outflow sheet, ing moderately abundant phenocrysts of typically accompanied by overlying tuff of sanidine and minor plagioclase, green cli­ Farr Ranch. Source unknown nopyroxene, biotite and opaque oxide, and Twft Datil Well Tuff and (or) tuff of Farr Ranch, trace apatite and zircon. Occurs locally in undivided (Eocene)—Mapped where only Old Horse Springs–New Horse Springs area one of the tuffs is present and identity is north of Plains of San Agustin; may correlate uncertain, or where both tuffs are present but with Tuff of Bishop Peak of similar age and too thin to map separately, as in northeast cor­ composition in Underwood Lake 7a-minute ner of Tularosa Mountains quadrangle quadrangle, Reserve-Luna area. Source Tac Basaltic lava flow of Alamocito Canyon unknown (Eocene)—Dark-gray, coarsely porphyritic basalt or andesite flow interlayered with vol­ Tpt Tuff of Bishop Peak (Ratté, 1989) (Eocene, caniclastic sedimentary rocks of Spears 34.6 Ma*, McIntosh and others, Group and overlain by Datil Well Tuff at 1992)—Thin, reddish-brown, dacitic ignim­ Alamocito Spring at Forks of Alamocito brite containing a moderate abundance of Creek. Thickness 0 to about 30 m plagioclase, sanidine, and biotite pheno­ crysts. Crops out mainly in northwestern part OLDER SEDIMENTARY ROCKS of Tularosa Mountains quadrangle, north of Luna, but has been tentatively identified else- Psgy Sedimentary rocks, undivided (Permian)—A where, as in region south and west of measured section (Stearns, 1962) on north Reserve. Source unknown side of Plains of San Agustin, in Horse Moun­ Tkt Kneeling Nun Tuff (Elston and others, 1975) tain East quadrangle, includes (ascending (Eocene, 34.9 Ma*, McIntosh and others, order) 201 ft (61 m) of Yeso Formation, 95 ft 1992)—Light-gray, rhyolite ignimbrite (29 m) of Glorieta Sandstone, and 417 ft (127 containing abundant quartz and sanidine m) of San Andres Limestone, all of Early phenocrysts, minor plagioclase and biotite, Permian age. Red sandstone associated with and accessory opaque oxides, sphene, brown this sequence was originally considered by

10 Stearns to be possibly Triassic, but is now J.M., and McIntosh, W.C., eds., Mogollon Slope, thought to belong with volcaniclastic sedi­ west-central New Mexico and east-central Arizona: mentary rocks of Spears Group New Mexico Geological Society Guidebook, 45th Annual Field Conference, 1994, p. 125–134. REFERENCES CITED Deal, E.G., and Rhodes, R.C., 1976, Volcano-tectonic struc­ tures in the San Mateo Mountains, Socorro County, New Bornhorst, T.J., 1976, Volcanic geology of the Crosby Moun­ Mexico, in Elston, W.E., and Northrup, S.A., eds., Cen­ tains and vicinity, Catron County, New Mexico: Albu­ ozoic volcanism in southwestern New Mexico: New querque, University of New Mexico, M.S. thesis, 113 p. Mexico Geological Society Special Publication 5, p. Bove, D.J., 1990, Preliminary geologic map of the Eagle 51–56. Peak quadrangle, Catron County, New Mexico: Duffield, W.A., and Dalrymple, G.B., 1990, The Taylor U.S.Geological Survey Open-File Report 90–0546, Creek Rhyolite of New Mexico—A rapidly emplaced scale 1:24,000. field of lava domes and flows: Bulletin of Volcanology, Bove, D.J., Ratté, J.C., McIntosh, W.M., Snee, L.W., and v. 52, p. 475–487. Futa, K., 1995, The evolution of the Eagle Peak Vol­ Elston, W.E., 1957, Geology and mineral resources of Dwyer cano—A distinctive phase of Middle Miocene volcan­ 15' quadrangle, Grant, Luna, and Sierra Counties, New ism in the western Mogollon-Datil volcanic field, New Mexico: New Mexico Bureau of Mines and Mineral Mexico: Journal of Volcanology and Geothermal Resources Bulletin 36, 86 p. Research, v. 69, p. 159–186. ———1976, Glossary of stratigraphic terms of the Mogol­ Cather, S.M., Chamberlin, R.M., and Ratté, J.C., 1994, Ter­ lon-Datil Volcanic Province: New Mexico Geological tiary stratigraphy and nomenclature for western New Society Special Publication 5, p. 131–145. Mexico and eastern Arizona, in Chamberlin, R.M., Kues, ———1984, Mid-Tertiary ash-flow tuff cauldrons, south- B.S., Cather, S.M., Barker, J.M., and McIntosh, W.C., western New Mexico: Journal of Geophysical Research, eds., Mogollon Slope, west-central New Mexico and p. 8733–8750. east-central Arizona: New Mexico Geological Society ———1989, Overview of the Mogollon-Datil Volcanic Guidebook, 45th Annual Field Conference, 1994, p. Field: New Mexico Geological Society Memoir 46, p. 259–266. 43–46. Chamberlin, R.M., Cather, S.M., Anderson, O.J., and Jones, Elston, W.E., Seager, W.R., and Clemons, R.E, 1975, Emory D.E., 1994, Reconnaissance geologic map of the Que­ Cauldron, Black Range, New Mexico—Source of the mado 60' Z 30' quadrangle: New Mexico Bureau of Mines Kneeling Nun Tuff, in Seager, W.R., Clemons, R.E., and and Mineral Resources Open-File Report, scale Callender, J.F., Guidebook of the Las Cruces Country: 1:100,000. New Mexico Geological Society, 26th Annual Field Chamberlin, R.M., 1994, "The Crosby Mountain "caldera"; A Conference, 1975, p. 283–292. volcano-tectonic collage of disparate origin" in "First day Jones, D.P., 1980, Volcanic geology of the Alegres Mountain road log," New Mexico Geological Society Forty-Fifth area, Catron County, New Mexico: Albuquerque, Uni­ Annual Field Conference, p. 16–18. versity of New Mexico, M.S. thesis, 76 p. Chapin, C.E., Chamberlin, R.M., Osburn, G.R., White, Lawrence, V.A., 1985, A study of the Indian Peaks tin-bearing D.W., and Sanford, A.R., 1978, Exploration framework rhyolite dome-flow complex, northern Black Range, of the Socorro geothermal area, New Mexico: New New Mexico: Boulder, University of Colorado, M.S. Mexico Geological Society Special Publication 7, p. thesis, 112 p. 115–129. Lawrence, V.A. and Richter, D.H., 1986, Geologic map of the Coney, P.J., 1976, Structure, volcanic stratigraphy, and gravity Indian Peaks West quadrangle, New Mexico: U.S. Geo­ across the Mogollon Plateau, New Mexico, in Elston, logical Survey Miscellaneous Field Studies Map W.E., and Northrup, S.A., eds., Cenozoic volcanism in MF–1849, scale 1:24,000. southwestern New Mexico: New Mexico Geological Lopez, D.A., and Bornhorst, T.J., 1979, Geologic map of the Society Special Publication 5, p. 29–41. [Figure 1 is a Datil area, Catron County, New Mexico: U.S. geologic map at approximate scale 1:125,000.] Geological Survey Miscellaneous Investigations Series Crews, S.G., 1990, Structure, syntectonic sedimentation, and Map I–1098, scale 1:50,000. stratigraphy of asymmetical non-marine basins: Markgraf, Vera, Bradbury, J.P., Forester, R.M., McCoy, W., Laramie, University of Wyoming, Ph.D. dissertation, Singh, G., and Sternberg, R.S., 1983, Paleoenviron­ 196 p., 77 figures. mental reassessment of the 1.6-million-year-old record ———1994, Tectonic control of synrift sedimentation pat- from San Agustin Basin, New Mexico: New Mexico terns, Reserve graben, southwestern New Mexico, in Geological Society Guidebook, 34th Field Confer­ Chamberlin, R.M., Kues, B.S., Cather, S.M., Barker, ence, Socorro Region II, p. 291–297.

11 Markgraf, Vera, Bradbury, J.P., Forester, R.M., Singh, G., and Ratté, J.C., Bove, D.J., Cather, S.M., Chamberlin, R.M., Sternburg, R.S., 1984, San Agustin Plains, New Mex­ Crews, S.G., and McIntosh, W.C., 1994, Third-day road ico—Age and paleoenvironmental potential, reassessed: log, from Alpine, Arizona, to Luna, Reserve, Apache Quaternary Research, v. 22, p. 336–343. Creek, Horse Springs and Datil, New Mexico, in Cham­ Marvin, R.F., Naeser, C.W., Bikerman, M., Mehnert, H.H., berlin, R.M., Kues, B.S., Cather, S.M., Barker, J.M., and and Ratté, J.C., 1987, Isotopic ages of post-Paleocene McIntosh, W.C., eds., Mogollon Slope, west-central igneous rocks within and bordering the Clifton 1° Z 2° New Mexico and east-central Arizona: New Mexico quadrangle, Arizona–New Mexico: New Mexico Geological Society Guidebook, 45th Annual Field Con­ Bureau of Mines and Mineral Resources Bulletin 118, ference, 1994, p. 79–111. 63 p. Ratté, J.C., Bove, D.J., and McIntosh, W.C., 1994, Geologic McIntosh, W.C., and Chamberlin, R.M., 1994, 40Ar/39Ar map of the Milligan Mountain quadrangle, Catron geochronology of middle to late Cenozoic ignimbrites, County, New Mexico: U.S. Geological Survey Geologic mafic lavas and volcaniclastic rocks in the Que­ Quadrangle Map GQ–1736, scale 1:24,000. mado-Datil region, New Mexico, in Chamberlin, R.M., Ratté, J.C., and Gaskill, D.L., 1975, Reconnaissance geologic Kues, B.S., Cather, S.M., Barker, J.M., and McIntosh, map of the Gila Wilderness Study Area, U.S. Geological W.C., eds., Mogollon Slope, west-central New Mexico Survey Miscellaneous Geologic Investigations Map and east-central Arizona: New Mexico Geological Soci­ I–886, scale 1:62,500. ety Guidebook, 45th Annual Field Conference, 1994, p. Ratté, J.C., McIntosh, W.C., and Houser, B.B., 1990, Geo­ 165–186. logic map of the Horse Mountain West quadrangle, McIntosh, W.C., Chapin, C.E., Ratté, J.C., and Sutter, J.F., Catron County, New Mexico: U.S. Geological Survey 1992, Time-stratigraphic framework for the Eocene-Oli­ Geologic Quadrangle Map GQ–1685, scale 1:24,000. gocene Mogollon-Datil volcanic field, southwest New Ratté, J.C., and Modreski, P.J., 1989, Days 3 and 4—Selected Mexico: Geological Society of America Bulletin, v. 104, volcanic features of the western Mogollon-Datil volca­ p. 851–871. nic field, in Chapin, C.E., and Zidek, J., eds., Field McIntosh, W.C., Kedzie, L.L., and Sutter, J.F., 1991, Paleo­ Excursions to volcanic terranes in the western United magnetism and 40Ar/39Ar ages of ignimbrites, States, Volume 1—Southern Rocky Mountain Region: Mogollon-Datil volcanic field, southwestern New New Mexico Bureau of Mines and Mineral Resources Mexico: New Mexico Bureau of Mines and Mineral Memoir 46, p. 68–91. Resources Bulletin 135, 79 p. Ratté, J.C., Modreski, P.J., McIntosh, W.C., and Chamber­ McIntosh, W.C., Sutter, J.F., Chapin, C.E., Osburn, G.R., and lin, R.M., 1994, The Horse Springs Dacite—An Ratté, J.C., 1986, A stratigraphic framework for the enigmatic pyroclastic deposit at the edge of the Plains Mogollon-Datil volcanic field based on paleomagnetism of San Agustin, in Chamberlin, R.M., Kues, B.S., and high precision 40Ar/39Ar dating of ignimbrites—A Cather, S.M., Barker, J.M., and McIntosh, W.C., eds., progress report, in Clemons, R.E., King, W.E., and Mogollon Slope, west-central New Mexico and Mack, G.H., eds., Truth or Consequences Region: New east-central Arizona: New Mexico Geological Society Mexico Geological Society Guidebook, 37th Annual Guidebook, 45th Annual Field Conference, 1994, p. Field Conference, 1986, p. 183–195. 193–207. New Mexico Geological Society, 1982, New Mexico high- Rhodes, R.C., and Smith, E.I., 1976, Stratigraphy and struc­ way geologic map, scale 1:1,000,000. ture of the northwestern part of the Mogollon Plateau Osburn, G.R., and Chapin, C.E., 1983, Nomenclature for Volcanic Province, in Elston, W.E., and Northrup, S.A., Cenozoic rocks of northeast Mogollon-Datil volcanic eds., Cenozoic volcanism in southwestern New Mexico: field, New Mexico: New Mexico Bureau of Mines and New Mexico Geological Society Special Publication 5, Mineral Resources Stratigraphic Chart 1, 1 folded sheet p. 57–62. [Figure 2 is a geologic map at approximate and 7-p. pamphlet. scale 1:100,000.] Ratté, J.C., 1980, Geologic map of the Saliz Pass quadrangle, Richter, D.H., 1987, Geologic Map of the O Bar O Mountain Catron County, New Mexico: U.S. Geological Survey East quadrangle, Catron County, New Mexico: U.S. Miscellaneous Field Studies Map MF–1203, scale Geological Survey Miscellaneous Field Studies Map 1:24,000. MF–1976, scale 1:24,000. ———1989, Geologic map of the Bull Basin quadrangle, Richter, D.H., and Lawrence, V.A., 1989, Geologic map of Catron County, New Mexico: U.S. Geological Survey the O Bar O Canyon West quadrangle, Catron County, Geologic Quadrangle Map GQ–1651, scale 1:24,000. New Mexico: U.S. Geological Survey Miscellaneous ———1992, Preliminary geologic map of the Tularosa Can- Field Studies Map MF–2075, scale, 1:24,000. yon quadrangle, Catron County, New Mexico: U.S. Geo­ Smith, E.I., 1976, Structure and petrology of the John Kerr logical Survey Open-File Report 92–187, scale Peak dome complex, southwestern New Mexico in 1:24,000. Elston, W.E., and Northrup, S.A., eds., Cenozoic

12 volcanism in southwestern New: New Mexico Geologi­ 78, 46 p. [Includes geologic map at 1:63,360 scale.] cal Society Special Publication 5, p. 71–78. Weber, R.H., and Willard, M.E., 1959, Reconnaissance geo­ Smith, E.I., and Rhodes, R.C., 1974, Squirrel Springs logic map of the Reserve 30' quadrangle: New Mexico volcano-tectonic depression—A buried cauldron in Bureau of Mines and Mineral Resources Geologic Map southwestern New Mexico: Geological Society of 12, scale 1:126,720. America Bulletin, v. 85, p. 1865–1868. Willard, M.E., and Stearns, C.E., 1971, Reconnaissance geo­ Stearns, C.E., 1962, Geology of the north half of the Pelona logic map of the Pelona 30 minute quadrangle: New 30' quadrangle, Catron County, New Mexico: New Mexico Bureau of Mines and Mineral Resources Mexico Bureau of Mines and Mineral Resources Bulletin Geologic Map 23, scale 1:126,720.

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