EagleNest-Granite Hillarea, Luna Gounty, - a newlook at some old rocks byWilliam R. Seagerand Greg H. Mack,Earth Sciences Dept., New Mexico State University, Las Cruces, NM 88003

Introduction covered by seemingly endlessexpanses of ern Luna County approximately30 km (19 The western perimeter of the West Potrillo sand, and onlv here and there do isolated mi) northeastof Columbus (Fig. 1). Mountains is a remote, desolateland with hills of bedroci projectabove the sanddrifts. Perhapsbecause of their remoteness,these few roads, few visitors, and few outcrops. Two of the more prominent hills are Eagle hills are not well known, even though they Waterless and treeless, much of the area is Nest and Granite Hill. locatedin southeast- have been visited occasionallyby geologists for more than 80 years.Published accounts are varied, contradictory, and brief, al- though an excellentrecent M.S. thesis pre- senteddetails of the geologyof Granite Hill (Broderick, 1984).There seem to be long standing disagreementsamong previous Aden Hllls : !s J workers about the generalage and structure ,'t: \Provldence Cone' of rocks at EagleNest and Granite Hill. In 1915Darton portrayed EagleNest out- crops as Pennsylvanianin age, whereasthose at Granite Hill, one kilometer farther east, he consideredto be Tertiary "agglomerate" intruded by Tertiarygranite porphyry. Dane and Bachman(1965) concurred with the Ter- tiary-ageassignment of the graniteat Gran- Aden volcano INDEX MAP OF NEW MEXICO z l J ioTo .,:,,:l 1i + J1 Alsoin this issue ,,,i Indexto NMGS guidebook papers on hydrology and related topics p.8 TommyLee Finnell(1923-1989) p. 14 East Potllllo NMGS spring meeting p. 14 tinorintalns Noticeof transferof NMBMMRfossil cephalopodspecimens ro coDiF figured by RousseauH. W MEXICO To El Paso Flower p.15 Mountaln MEXTCO Potrlllo maar NMGS 1989 abstracts p.16 Service/News p.18 SCALE NMBMMRMineralMuseum 5 10 mlles Fund p. 19 15 kllometers I Staff notes p.20 ?,. nto Gomingsoon SugariteCanyon State Park Mineraland mineral-fuelproduction ]!Pemox No. 1 Moyotes Y 't6,217', activitiesin NewMexico during Prscambrian 1988 Stratigraphyand structure of the FIGURE l-Location map of Eagle Nest-Cranite Hill area (from Seager,1989) The area of Fig. 9 is KlondikeHills shown by the rectangle. FIGURE 2-Eagle Nest ridge capped by cliff-forming Permian carbonates FIGURE 3-Gastropods and nautiloid in Colina (uppermost Hueco) For- above overtumed Lower Cretaceousstrata. Laramide thrust truncates car- mation at EagleNest. bonates at base of cliff. View looks northwestward.

ite Hill but consideredthe sedimentary rocks basement-coreduplift of the AncestralRock- cambrian basement of south-central New at both Granite Hill and Eagle Nest to be ies system,the Burro-Florida-Moyotes uplift Mexico. Recognizing this, Broderick (1984) Cretaceous.Hoffer (1976)agreed with Dane resulted in erosion of various thicknessesof and Broderick et al. (1986)assigned the gran- and Bachman's(1965) age assignments of the pre-mid-Wolfcampian strata and, perhaps ite a Precambrian age, a correlation with which rocks in both outcrops. However, in 1981 locally, nondeposition of Pennsylvanian we concur. Hoffer and Hoffer reported the sedimentary strata. According to Broderick (1984) the granite rocks at Granite Hill to be Early Cretaceous, In Early Cretaceous time the Eagle Nest contains 55-607o anhedral orthoclase micro- and in 1983Hoffer and Hoffer assigned the areawas part of the rift basin of Mack et al. perthite, and 35-40Vo anhedral quartz. Ser- entire section at EagleNest to the Early Cre- (1986; 1988) that filled with arkosic marine icite, pyrite, and hematite are common taceousand consideredit to be right sideup. and nonmarine sediments. Granitic rift secondary minerals. The granite contains ap- They recoveredLower Cretaceousfossils from shoulders along the northern and north- proximately 73VoSiO, (Broderick et al., 1986). part of the Eagle Nest section.Mack et al. eastern margins of the rift furnished much (1986)also believed that the Lower Creta- of the arkosicsediment. ceousstrata at EagleNest were right side up In Laramidetime (LateCretaceous to early but additionally recognizedthat an upper, Tertiary) both Eagle Nest and Granite Hill New AAexnc@ massive, cliff-forming limestone was sepa- were part of a zone of thrusting, basement- rated from lower beds by a low-angle fault. coreduplifts, and basinformation extending Broderick (1984)mapped Granite Hill and from west Texasnorthwestward into south- GEOLOGY considered the granite to be Precambrianin easternArizona. Controversycontinues over . SGaenGeand Service age, overlain by Lower Cretaceousarkosic the dominant style of deformation in this re- Volums 12, No. 1, February 1990 strata; this view was repeated by Broderick gion: regional overthrusting or foreland-style Editor:Carol A. Hiellming Draftingassistance: Rebecca Titus et al. (1986). basement-blockuplifts (e.9. Drewes, 1978; Publishedquarterly by Our interpretations of Granite Hill and Davis, 7979;Seager and Mack, 1985). New Mexico Bureauof Mines and Mineral Resources Eagle Nest differ significantly from previ- Finally, both Eagle Nest and Granite Hill a division of New Mqir Irutitute of Mining & llthnd%y ously published accounts.In this report we BOARD OF REGENTS are part of the late Tertiary CamelMountain Ex Officio presentevidence that Lower Cretaceousstrata fault block (Seager,1989), one of the many Garrey Canuthers, Gopernorof Nrut Menco at EagleNest are upsidedown and that they fault-block uplifts in the southern part of the Alan Morgan, Sulvilltendent of Publiclnstruclnn Appointed are overlain by a thrust sheetof Permian car- Rio Granderift. Tilted eastward15 to 20 de- Lenton Malry, Pra ,1985-1991,Albuquerque bonates.Right-side-up sedimentary strata at grees, the Camel Mountain fault block is Robert O Andemo^, S{ lTrcas,1 7-1993, Roswell Lt Cen Leo Marquez, 1989-1995,Alhuquerquc Granite Hill, which nonconformably overlie nearly buried by Quaternary sand and ba- Carol A Rymer, M D 1989-1995,Albuqueryuc Precambrian granite and are intruded by salt. Stmcturally high hills such as EagleNest Steve Torres, 1967-1991,Allruqileryut middle Tertiary(?) dikes, are latest New Mexico lnstitute of Mining & Technology Creta- and Granite Hill, as well as the prominent Pr$idqt laurence H littman ceousor early Tertiary in age.The two hills, Quaternary fault scarp along the westem New Mexico Bureau of Mines & Mineral Resures Eagle Nest and Granite Hill, are separated margin of the block (Camel Mountain es- Directornnd StntcGeolosist Frank E Kottlowski M. Robe?tson by a major fault zone whose geometry and carpment,Fig 1.), the geo- Aswiate Dircctol James constitutesome of Subrriptions: lssued quarterlt February, Mat AuSust, history of movement are somewhat specu- logic evidencefor the presenceand extentof November; subsription prie $6 0O/elendar year lative. These conclusionswere reported by the fault block. Editorialmtla: Articles submitted for publication should Seager(1989; in press). be in the editor's hands a minimum of five (5) months before date of publication (February,Mat August, or Stratigraphy November) and should be no longer than 20 tyPewrit- Regional setting ten, double-spacedpages All rientific papere will be reviewed by at least two people in the appropriate field The EagleNest-Granite Hill areais part of Precambrian rocks of study AddressinquiriG to CarolA Hiellming, Editor ot Nru Mexia Geology,New Mexico Bureau of Mines & four tectonic elements of different ages. It Brown to grayish-orangegranite crops out Mineral Resources,Saorc, NM 87801 may be within the Burro-Florida-Moyotes along the western base of Granite Hill. Al- Publshed as public tloruifl, ther4ore reprcdrciblewithout pa- uplift of mid-Wolfcampanian age (Kottlow- though interpretedas Tertiary in ageby some mission Sourcecredit requ5ted ski 1950; 1963; Navarro and Tovar, 1975; previous workers (Darton, 1916;Dane and Circulation:|,ffi Greenwoodet al.,1977;Wilson and fordan, Bachman, 1965; Hoffer, 1976), the coarse- Prirfer: University of New Meico Printing Plant 1988;Thompson et al. 1978;Seageg1989). A grained granite is typical of much of the Pre-

2 February 1989 Nal Mexico Geology FIGURE4-Nautiloid in Colina (uppermost Hueco) Formation at EagleNest. FIGURE S-Cephalopods in Colina (uppermost Hueco) Formation at Eagle Nest (below scale). The mineral composition, silica content, with the Yeso Formation and uppermost beds cates a Paleozoicage for the carbonate sec- and very coarse grained texture is consistent of the Hueco Formation of south-central New tion (D. V. LeMone, personalcommunication, with other Precambrian granitic rocks of Mexico (e.g., Kottlowski et al., 1956)and with 1989).The strata have none of the lithologic south-central New Mexico. It is strikingly the Epitaph and Colina Formations of south- characteristicsof lower to middle Paleozoic dissimilar in terms of texture and compo-si- western New Mexico (Zeller, 1965). strata in the region and are almost certainly tion to Tertiary-age stocks in the Tres Her- Cliff-forming, thick-bedded limestone of Permian. Rock types and fauna are most manas, Organ and |arilla Mountains, and the Colina (uppermost Hueco) Formation nearly like those seen in uppermost Hueco Cooke's Range. It also is dissimilar to the overlies the thrust fault. These massive, dark- strata in the El Paso area (D. V. LeMone, lower Paleozoic syenitic stocks of the Florida gray to blue-gray limestone beds are at least personal communication) and like those re- Mountains (Evans and Clemons, 1988). 750 m (492 ft) thick. Some horizons contain ported for the Colina Limestone of south- abundant chert nodules while other beds are Permian rocks western New Mexico (Zeller, L965). Consequently we tentatively assign this sec- tion to the Colina (uppermost Hueco) For- mation. Strata that we correlate with the Epitaph (Yeso)Formation occur conformably(?) above The presence of rugose corals and small the Colina (uppermost Hueco) Formation in Tentatively, we correlate the Permian section orthoconic nautiloids ( Mooreoceras(?))indi- the northernmost hills at Eagle Nest. Thin- to medium-bedded, cherty, dolomitic lime- stone is the common rock'type. Beds are al- ternately light gray to medium gray. Numerous siliceous"eyes" are common. Fossils are comminuted, silicified, and un- identified. Approximately 100 m (328 ft) of Epitaph (Yeso)section is exposed,although part of this is obscuredby sand.The baseof the formation also is covered by sand. Our assignmentof thesedoloinitic carbon- ates to the Epitaph (Yeso)Formation is based on physical correlation with similar dolo- mitic carbonatesin the East Potrillo Moun- tains (Seagerand Mack, in press) and the West Lime Hills of the TresHermanas Moun- tains. In the the do- lomitic carbonatescontain beds of soft, yellow sandstone and underlie massive carbonates thought to be SanAndres Limestone (Seager and Mack, in press). Dolomitic carbonatesin the West Lime Hills are lithologically similar to those of Eagle Nest and the East Potrillo Mountains and have yielded middle Permian (early Leonard) fossils (Thompson, 1982). Lower Cretaceousrocks Approximately 288 m (945 ft) of Lower Cretaceous sedimentary rocks are exposed east of Eagle Nest in the overturned limb of FIGURE 6-Overturned crossbeddingin sandstoneof sandstone-limestonemember of the U-Bar For- the syncline (Fig. 6). An Early Cretaceousage mation. for these rocks is based on the presencebf

Nm Mexico Geology February 1989 3 rudistid clams, which are restricted to Lower stone, sandstone-limestone,and upper (7 ft) of fossiliferous and intraclastic lime- Cretaceousrocks in southwesternNew Mex- limestone (Fig. 7). The upper contact of the stone separated by covered intervals. Also ico, and on lithologic correlation with Lower U-Bar Formation is coveredbeneath Quater- presentin the upper limestonemember are Cretaceousrocks in the East Potrillo Moun- nary alluvium. a few thin (<30 cm, 1 ft) beds of brown silt- tains (Fig. 7; ZeIler, 1965;Mack et al., t986; The lower limestone member of the U-Bar stone and very fine sandstone. Seager and Mack, in press). Lower Creta- Formation consistsof 8 m (26 ft) of thin (<30 The Lower Cretaceoussection at EagleNest ceous rocks at Eagle Nest are divided into cm, 1 ft) beds of gray and tan limestone con- correlatesin terms of rock type and thickness the Hell-to-Finishand U-Bar Formations(Fig. taining bivalvesand gastropods.The abun- with Lower Cretaceousrocks exposed30 km Z),a nomenclatureoriginally definedby Zeller dant, easilyrecognizable fossils in this member (19 mi) to the east in the East Potrillo Moun- (1965)in the Big Hatchet Mountains. are in sharp contrast to the micrite lime- tains (Fig. 7; Mack, 1986;Seager and Mack, At EagleNest the Hell-to-Finish Formation stones of the Hell-to-Finish Formation. The in press).The biggestdifference between these is 153 m (502ft) thick and is subdivided into lower limestone member is overlain by 12m stratigraphic sectionsis the coarsergrain size lower conglomerate and arkosic sandstone (39 ft) of siliciclastic rocks that include a of the arkosic sandstonemember of the Hell- members (Fig. 7). The lower conglomerate prominent 4-m-thick (13ft) ledge oI gray, fos- to-Finish Formation at EagleNest compared member is 30 m (98 ft) thick, although the siliferous, crossbedded, medium to coarse to the mottled siltstone member of the Hell- base is not exposed due to truncation by a sandstone.Also presentare severalthin (<1.5 to-Finish Formation in the East Potrillo fault. The conglomerate member is com- m, 5 ft) beds of fossiliferouspebble conglom- Mountains. Regional variations in grain size posedof beds 1.5 to 4.5 m (5 ft to 15ft) thick erate and gray, bioturbated, silty shale. The of the Hell-to-Finish Formation are common/ of grain-supported cobble and boulder con- sandstone member is overlain by the most however,in responseto localtectonism (Mack, glomerate.Clasts in the conglomerateare well distinctive marker bed in the U-Bar Forma- te87). rounded and consistof limestone,dolomite, tion, the rudistid limestone member. This chert, and sandstone. Conglomeratesare member consistsof large rudistid clams in Cretaceousto lower Tertiary rocks interbedded with red shale and thin (<1 m) growth position and ranles in thicknessfrom Upper micritic limestone. The upper member of the 3 to 15 m (10 to 49 ft). The sandstone-lime- Sedimentary rocks at Granite Hill (Fig. 8) Hell-to-Finish Formation is 123m (4m3ft) thick stone member is 75 m (246tt) thick, although are approximately 240 m (787 ft) thick and and is characterized by several distinctive the lower half is poorly exposed beneath can be separatedinto four members, follow- beds as much as 6 m (20 ft) thick of massive, Quaternary alluvium. Very fine to medium- ing Broderick(198a). The basalconglomerate pink, pebbly arkosic sandstone.Also present grained sandstone,gray shale, and fossilif- is16 m Q49 ft) thick and nonconformably are limestone and chert pebble and cobble erous limestoneconstitute this member.Very overlies Precambriangranite. The contactbe- conglomerate,thin (<1 m) (3 ft) micritic lime- fine to fine-grained sandstonesdisplay bur- tween the granite and conglomerate is dif- stone, and red silty shale. rows, hummocky cross stratification, and ficult to distinguish because bedding and The conformablecontactbetween the Hell- symmetrical ripple marks, whereas a 2-m- detrital texture are obscure in the conglom- to-Finish and U-Bar Formations is placed thick (7 ft), medium-grained sandstonenear erate and becausethe conglomerateconsists above the uppermost pink arkose. The ex- the top of the member is crossbedded(Fig. exclusively of clasts derived from the un- posed thickness of the U-Bar Formation is 5). Bivalve and gastropodfossils are common derlying granite. The basal conglomeratefines 135m (443f$. The unit is separatedinto five in the interbedded limestones. The upper upward from bouldersand cobblesto pebble members, which in ascendingorder are: the limestonemember (37 m thick, 121ft) is poorly conglomerateand pebbly sandstone.The lower limestone. sandstone.rudistid lime- exposed and consistsof beds as thick as 2 m basal conglomerate is overlain by 36 m (118

Eost PotrilfoMts

upper limestone Nest U-Bor siltstone- limesfone rudistidlimestone U-Bor limesfone sondsfone rudistidf imesfone -: sondslone lower lime

Helf- orkosic motfled s ondsfonc to- silfslone to-

Finish bosof oooooooooo Finish t: con lomerote FIGURE 7-Correlation of Lower Cretaceousrocks of Eagle Nest and East Potrillo Mountains.

February1989 NewMexico Geology ft) ofinterbeddedarkosic sandstone and sandy ship of the porphyritic andesite. Although taceousto lower Tertiary arkosic section and micritic limestone. No fossils were recog- this dike has not been radiometricallv dated. therefore are younger. Physically, the intru- nized in either rock type, although the sand- correlation with similar igneous iocks in sives are similar to other intermediate-com- stones contain a few straight to sinuous, southern New Mexico indicate that it is prob- position dikes, plugs, and stocks of south- horizontal burrows. The most distinctive ably no younger than middle Tertiary. central New Mexico that have been dated member is a lS-m-thick (49 ft) conglomerate In southern New Mexico, post-Lower Cre- Eoceneto Oligocenein age(Seagea in press). composed of well-rounded to subrounded, taceous and pre-middle Tertiary sedimen- grain-supported pebblesand cobbles.Clasts tary rocks can be divided into two distinct are primarily limestone and dolomite, al- sequences.The older sequenceis Late Cre- Structure though chert, sandstone, granite, and an- taceous in age (Cenomanian-early Campan- The structural contrastbetween EagleNest desite are also present. A few thin (<1 m) ian), consistsprimarily of mixed marine and and Granite Hill is no less striking than the lensesof sandstoneare intercalatedwithin nonmarine fine-grainedsandstone and shale, stratigraphic contrast. Figures9 and 10 illus- the conglomerate.The upper 113m (321ft) and includes the Dakota, Mancos, and Tres trate the different structural styles of the two of the section consistsof interbedded fine to Hermanos Formations and the Mesaverde outcrops. Granite Hill appears to be part of very fine sandstone, siltstone, and lime- (Mack Group et al., 1988).The upper se- a relatively simple northwest-trending base- stone. This member is poorly exposed and quence ranges from latest Cretaceousto ment-cored fault block tilted northeastward shale probably underlies many of the cov- Eocene in age and includes the Ringbone, (Fig. 8). EagleNest, on the other hand, is a ered intervals. Sandstoneand siltstone beds McRae, Lobo, and Love Ranch Formations segment of a thrust sheet of Permian strata (Clemons and Mack, 1988).The younger rocks that has moved east-northeast to override are entirely nonmarine in origin and display the overturned Lower Cretaceousrocks. a wide range in grain size from boulder con- As shown in Figure 10, the structure at glomerateto shale.The wide variation in grain Eagle Nest may be interpreted as a thrust size and the lack of evidencefor marine dep- sheet of strata in normal stratigraphic order is crosscutby a porphyritic andesitedike. osition suggestthat the sedimentaryrocks beneath which lies an overturned syncline. Despitethe lack of index fossils,sedimen- at Granite Hill correlatewith uppermost Cre- Vergence is toward the east-northeast and tary rocks at Granite Hill can be bracketed taceous-Eocenerocks. Indeed, the sedimen- the thrust fault strikes predominantly north- as post-Early Cretaceousand pre-middle Ter- tary rocksat GraniteHill most closelyresemble northwest. It dips southwest 30 to 40 degrees tiary. The sedimentary-clastconglomerate has the Lobo Formation exposedin the Florida and appears to be segmentedby at least two a few limestone cobblesthat iontain Orbi- Mountains (Mack and Clemons, 1988). east-striking tear faults. Both hanging-wall tolina, a foraminiferal genus that in south- and footwall strata are truncated by the thrust western New Mexico is found only in the (Fig. 11), but the stratigraphic separation Lower CretaceousU-Bar Formation (Zeller, Middle(?) Tertiary rocks across the fault is not known. In terms of 1965;Mack et al., 1986).Because there are Porphyritic andesite dikes crop out exten- both structural geometry and rock systems no unconformities within Lower Cretaceous sively at Granite Hill. According to Broderick involved in the deformation, the Eagle Nest strata in southwestern New Mexico, the sed- (1984) the rock consists largely of pheno- structure is nearly identical to the Laramide imentary rocks at Granite Hill probably post- crysts of andesine and biotite set in an deformation of the East Potrillo Mountains date not only the U-Bar Formition buf aho aphanitic matrix. The biotite is pseudo- 30 km (19 mi) to the east (Seagerand Mack, the overlying Mojado Formation. The upper morph after hornblende. in press). age limit of the sedimentary rocks at Grinite The porphyry dikes transectboth Precam- The structural relief between Granite Hill Hill is defined by the crosscuttingrelation- brian granite and the overlying Upper Cre- and Eagle Nest requires that the two out- crops be separated by a major fault zone, herein named Granite Hill fault (Figs. 9 and 10). Unfortunately, the fault is not exposed. It clearly is downthrown to the west and seemingly trends northwest; whether it is normal, reverse, or thrust is not known. In Figure 10we show the fault to be normal and steep because the tilted footwall strata of Granite Hill show no indication of compres- sional-stylefolding as they approachthe fault zone. If the fault is Laramide in age, how- ever, it may be a thrust or reverse fault that dips northeast rather than southwest. The age of the fault also is uncertain. Sev- eral possibletimes of movement can be in- ferred on the basisof structuralor shatigraphic grounds, but none is well constrained: 1) Uplift in Early Cretaceous time. This possibility is suggestedby the coarsetongues of granitic detritus in the Hell-to-Finish For- mation of the Eagle Nest area, which may have been derived from uplifted Precam- brian granite at Granite Hill. However, the arkose may also have been washed from a more distant, different fault block or from a more distant segmentof the Granite Hill block. If the Granite Hill block were the source of thesearkoses, the block could havebeen either an intrarift fault block or the bounding rift FIGURE 8-Granite Hill. View looks northward. Precambriangranite crops out on left (west) margin shoulder. Furthermore, the Granite Hill fault of hill. Arkosic strata correlative with the Upper Cretaceous-loier Tertiary Lobo Formation dip to ihe block surely was buried later in the Early right (east) and form the rest of the hill. Cretaceousby carbonatesof the U-Bar For-

Nan Mexico Geology February 7989 5 SCALE o 0.5 mi. o tkm'

Pc Tear fault Thrustfault, dotted where concealed Normalfault, dotted where concealedor inferred

T.27S.

anlte Hill +qJlSru KhzT Lz

R.5w. colum - ---- ,1 ,o' ranchand 9-:2 ""=d --"a€ ===='-' 4?,---'i'=-'- ./z- FIGURE 9--4eologic map of EagleNest-Granite Hill area. p€g, Precambriangranite; Pc, Permian Colina Formation; Pe, Permian Epitaph Formation; Kh, Lower CretaceousHell-to-Finish Forrnation; Ku, Lower CretaceousU-Bar Formation; KT, Upper Cretaceous-lowerTertiary arkosic sedimentary rocks;Ti, Middle(?)Tertiary intermediate-compositionintrusives; Tb, Tertiary basalt;Q, Quaternarysand and alluvium; Qc, colluvium.

W \E SW NE

Eagle Nest Granlte Hill Eleu(ft.)[ Bend in section A' 4500 o 4200 ";;iJi-)th>Ts 3900 q#J',ti,'; 3600 Ku ,.' Ku(?) ,I 330 '1;;t'it Sil,+I):.*-i' 3000 P 2700 tll^ I I I FIGURE lO-Geologic cross section through Eagle Nest and Granite Hill. SeeFig. 9 for line of section. Symbols same as Fig. 9, except P indicates undifferentiated Permian or older rocks.

February 1989 New Mexico Geology mation becausethese sediments contain lit- tle or no locally derived arkosic strata. 2) Uplift in Laramidetime. Figure 10shows that fault truncation of Lower Cretaceous strata is required by the structuralrelation- ships at Granite Hill and Eagle Nest. This

presumably by movement along the fault in question. Of the three possible times of movement of the Granite Hills fault, Lar- amide movementseems best constrained bv available evidence. 3) Late Tertiary movement. The site of Laramide uplift at Granite Hill eventually evolved into a Laramide basin as evidenced by the thick accumulationof upward-fining laramide sediments.The basinis now uplifted and deeply eroded as a result of eitlier re- newed late Tertiary movementon the Gran- ite Hills fault or uplift and eastwardtilting of the Camel Mountain fault block, or bothl

Conclusions FIGURE ll-Permian Colina (uppermost Hueco) Formation in thrust sheet at Eagle Nest. Note trun- - Although uncertaintiesremain concerning cation of bedding at thrust, which follows baseof cliffs. Rudistid limestone membei of U-Bar Formation the geologic relationships between Granite forms outcrops in foreground and is overturned. Hill and EagleNest, severalconclusions now seemclear. Lower Cretaceousrocks exposed at EagleNest can be correlatedwith the Hell- to-Finishand U-Bar Formationsof the late Tertiary are other possible,but poorly Mountains: American Journal of Science,v. 288, pp. Little 735-755. Hatchet and East Potrillo Mountains area. constrained, times of fault movement. AcxNowr-rpcMENrs-We Greenwood, E , Kottlowski, F 8., and Thompson, S., ilI, Approximately 288 m (945 ft) thick, these thank David V. l9Z, Petroleum potential LeMone, and stratigrapliy of Pedre- Lower Cretaceousstrata form the over- University of Texasat El Paso, for gosa Basin: comparison with Permian and Orogrande his turned limb of a major syncline. Above the aid in identifying photographsof fossils basins: American Association Peholeum Geologists, Bulletin, v. 51, no. 9, pp. 1,M8-7469. inverted Lower Cretaceousrocks, a thrust from EagleNest. Discussionswith Tim Law- ton, New Mexico State University, helped Hoffer, J. M., 7976,Geology of Potrillo basaltfield, south- plateof Permianstrata consists of carbonates central New Mexico: New Mexico Bureauof Mines and our understanding of the structure and slra- Mineraf Resources,Circular 149,30 pp. tigraphy and we are grateful to him. We also Hoffer, R. L., and Hoffer, J. M., 7981,,A note on Lower appreciatethe helpful reviews of this manu- Cretaceousoutcrops, southeasternLuna County, New script by Lawton Mexico:El PasoC,eblogical Society, Guidebook 1981 Field and LeMone,and by Frank Conference,pp Kottlowski, 54-56 New Mexico Bureau of Mines Hoffer, R. L., and Hoffer, J.M ,1983, Cretaceousstratig- Thrust faulting at EagleNest was directed and Mineral Resources.The New MexicoBu- raphy of south-centralNew Mexicoand northernChi- huahua, Mexico: El PasoGeological Society, east-northeastand is Laramidein style.Total reau of Mines and Mineral Resourcesfinan- Guidebook cially supported this study, and we thank 1983Fiefd Conference, pp.249-253 displacementis in doubt but may 6e signif- Kottlowski, F. E , 1960,Summarv of Pennsylvaniansec- icant. this institution and Frank E. Kottlowski. tions in southwestem New lr,iexicoand southeastern At Granite Hill an upward-finins, risht- Director, for their continued support. Arizona: New Mexico Bureau of Mines and Mineral Resources, side-up sequenceof arkosic Bulletin 56, 198 pp and c6ngl6m- Kottfowski, F. E., 1963,Paleozoic and Mesozoicstrata of erate strata overlie Precambrian granite. At southwest and south-centralNew Mexico:New Mexico least 240 m (787ft) thick, basalparts of the References Bureau of Mines and Mineral Resources,Bulletin 79, Broderick, J. C., 1984,The geology of Granite Hill, Luna 100 pp County, New Mexico: Un"publiihedMS thesis, Univer- Kottlowski, F. E., Flower, R. H., Thompson, M L., and Foster, W., _ sity of Texasat El Paso,Texas, 89 pp. R l9%, Stratigraphic studies of the San Broderick,J. C., Hoffer, R. L., and-Hoffer,l. M., 79ff6, Andres Mountains, New Mexico: New Mexico Bureau of Mines and Mineral Resources,Memoir 1, 132pp. Mack, G. H., 7986, Lower Cretaceousshatigraphy and depositional envhonments in the East Potrillo Moun- tains and adiacentareas of southwesternNew Mexico: mation of the area. El PasoGeological Society, Guidebook 1986Field Con- ference,pp. 85-94. Mack, G. H., 1987,Mid-Cretaceous (late Albian) change from rift to retroarc foreland basin in southwestem New Mexico: GeologicalSociety of America, Bulletin, v. 98, no 5, pp. fl7-51.4. Mack, G H, and Clemons, R 8., 1988,Structural and stratigraphic evidencefor the Laramide(early Tertiary) Burro uplift in southwesternNew Mexico:New Mexico 279, pp A3-569. Geological Society, Guidebook to 39th Field Confer- Drewes, H., 1978,The cordilleran orogenic belt between ence,pp.59-66. Nevadaand Chihuahua;Geological Society ofAmerica, Mack,G. H., Galemore,J. A., and Kaczmarek,E.L ,7988, Bulletin, v. 89, pp. Ul- 657. Cretaceousforeland basin in southwestern New Mex- Evans, K. V., and Clemons, R. E., 1988, Cambrian- ico: New Mexico GeologicalSociety, Guidebook to 39th Ordovician (500Ma; alkalic plutonism in southwestern Field Conference, pp. 135-742. tion. Uplift during the Early Cretaceous and New Mexico: U-Th-Pb isotopic data from the Florida Continued on p. 19

Nm Mexico Geology February 1989 Mohammed, K., and Hussain, M., 1989,Brush- ite----occurrenceof an unusual phosphate min- eral in Castile evaporites:West Texas Geological Sociefy,Bulletin, v.29, no.3, pp.5-7. Roybal,G. H., Campbell,F. W., Beaumont,E. C., Bellis,D., Kottlowski,F E., and Cohen,A. D., 1989-Quality assessmentof strippable coals in New Mexico, year III, phase II, Menefee, Cre- vasseCanyon, and Moreno Hill Formation coals in the San Juan Basin and Salt Lake coal field: New Mexico Researchand Development Insti- _ tute, Rept. NMRDI 2-76-5310,700'pp. Stone, W. J.,_!9Q.Mining in a multiple land-use area of the American Southwest----conflictor co- edstence?, ln Environmental planning in mul- tiple land useareas, B. Richards,D. Dundas,J. Robertson,and G. Ian, editors:llth North Aus- tralian Mine Rehabilitation Workshop, Proceed- ings, pp. 741-747.

sociation of Petroleum Geologists, Bulletin, v. . 73, no. 108, pp. 152-158. q) _WoldeGabriel,G., and Goff, F., 1989,Temporal relations of volcanism and hydrothermaf sys- tems in two areas of the Jem'ezvolcanic fieid, New Mexico: Geology,v. 77, no. lI, pp.986- 989.

0pen-filereports I{MBMMRMineral Museum ilotes Continuedfrom p. 7 NMBMMR MuseumFund Mack, G H., Kolins, W B , and Galemore,I A., 1986, Lower Cretaceousstratigraphy, depositional envhon- *358-Geology of Winston Ttlz' quadrangle,Sierra Amateur gem and mineral societiesof New ments, and sediment dispersal in southwestem New County,_NewMexico,byR. W. Harrison,17pp., Mexico have recently establishedan endow- Mexico: American Journal of Science,v 285, pp 309- 331. 2 reproducible map sheets. $6.40 ment fund for the New Mexico Bureau of '360-Mineral Navarro, A., and Tovar, 1975, Stratigraphy and tec- resourcesof the Grav Ranch J , area. Mines and Mineral ResourcesMineral Mu- tonics of the state of Chihuahua; in Hills, M. (ed Hidllgg County, I ), New Mexico,by'S. Thompson seum. Spearheadedby the Chaparral Rock- Exploration from the mountains to the basin: El Paso III, R. W Eveleth,and J. M. Barker,1989, 48 hounds of Roswell and the Los Alamos GeologicafSociety, pp 23-27. PP' $9.60 GeologicalSociety, the BureauMuseum Fund Seager,W. R, 1989, Geology beneath and around the West Potrillo basalts:New Mexico Geology, v 11, no is designedto provide the museumwith funds USGS 3, pp. s3-s9 for the purchase of display-quality New Seager,W. R., in press,Geology of the southwesternpart 87-568-Characteristics and trends of streamflow Mexico mineral and gem specimens.Funds of the Las Crucesand northwestem part of the El Paso 1' x 2" sheets:New Mexico and dissolved solids in the upper Colorado River donated to the Bureau Museum Fund are Bureauof Mines and Min- eral ResourcesGeologic Map basin, Arizona, Colorado, New Mexico, Utah, invested through the New Mexico Tech Re- Seager,W. R., and Mack, G. H., 1986,Laramide paleo- and Wyoming, by T. D. Liebermann, D. K. searchFoundation at New Mexico Institute tectonics of southem New Mexico; iz Peterson, f. A. Mueller, f . E. Kircher, and A. F. Choquette,1989, of Mining and Technology;the earnings will (ed.), Paleotectonicsand sedimentation in the Rocky 99 Mountain region: American Association of Petroleum *88-490-Variable-densityPP. be used for specimenacquisition. All dona- ground-water fl ow and Geologists, Memoir 41, pp.669-685 tions made to the BureauMuseum Fund, as paleohydrologyin the WasteIsolation Pilot Plant Seager,W. R., and Mack, G. H., in press,Geology of the (WIPP) region, southeasternNew Mexico, by P. well as those made directlv to the museum, EastPohillo Mountains and vicinity, DofraAna County, B. Davies,1989,752 pp are tax deductible.The BureauMuseum Fund New Mexico:New Mexico Bureauof Mines and Mineral $36.40 ResourcesBulletin 89-26-Conversion and comparison representsthe first step in the Bureau'splans of the math- Thompson, 5., ilI, 7982,Oil and gas exploration ematical, wells in three-dimension-al,finite-difference, for remodeling and expanding the Mineral southwesternNew Mexico; in Powers,R B (ed.), Geo- ground-water flow model to the modular, three- Museum. logic studies of the Cordilleran thrust belt: Rocky dimensional, finitedifference, ground-water flow Persons interested in making a tax- Mountain Associationof Geologists,pp. 521-536. model for the Tesuqueaquifer system in north- deductibledonation to the BureauMuseum Thompson, S., ilI, TovarR , J. C., and Conley,I N., 1928, ern New Oil and gas exploration in the Pedregosabasin: New Mexico, by A. M. J. Umari and T. L Fund should make checks Szeliga, 1989,39 pp payableto the New Mexico Geological Society, Guidebook to 29th Field Mexico Tech Conference, *89-498-Stratigraphic and sedimentologic stud- ResearchFoundation, Bureau pp 331-342. Wilson, L., and C. F, 1988,Late ies of the Twowells Tongueof the Dakota Sand- Museum Fund. Checksshould be sentto the J. Jordan, Jr, Paleozoic- early Mesozoic rifting in southern New Mexico stone, southern Alumni and Development Office, New Mex- and San Juan Basin, New Mexico, northern Mexico: controls on subsequentplatform de- by I. r. Dillinger, 7989,29 pp. $5.80 ico Institute of Mining and Technology, velopment; ir Robichaud, S. R., and Gallick, C. M. Socorro, New Mexico 87801.For more infor- (eds.), Basin to shelf faciestransition of the WolfcamD- USBM mation on the BureauMuseum Fund or other ian stratigraphy of the Orogrande basin:Pemian Basin aspectsof the Mineral Museum, contact the Section-SEPM,Pub. no 88-28, pp 79-88. Zeller, R. A., Jr., 7965, Stratigraphy of the Big Hatchet Minerals yearbook 7987-v. II, area reports-do- Bureau'sMineralogist and Curator,Marc L. Mountains area:New Mexico Bureauof Mines and Min- mestic, 1989, 439 pp. Wilson, (505)835-5246. eral Resources,Memoir 15, 128 pp. D

Nm Mexico Gmlogy Rebruary 1989