Late Wisconsin Climate Inferences from Rock Glaciers in South-Central

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LateWisconsin climatic inlerences from rock glaciers in south-centraland west-central New Mexico andeast-central Arizona byJohn W. Blagbrough, P0 Box8063, Albuquerque, NewMexico 87198

Abstract

Inactive rock glaciersof late Wisconsin age occur at seven sites in south-central and west-central New Mexico and in east-centralArizona. They are at the base of steep talus in the heads of canyons and ravines and have surfacefeatures indicating they are ice-cemented (permafrost) forms that moved by the flow of interstitial ice. The rock glaciersindicate zones of alpine permafrost with lower levels that rise from approximately 2,400m in the east region to 2,950 m in the west. Within the zones the mean annual temperaturewas below freezing, and the climatewas marked by much diurnal freezing and thawing resulting in the production of large volumes of talus in favorableterrain. The snow cover was thin and of short duration, which favored ground freezing and cryofraction. The rock glaciers in the east region occur near the late Wisconsin 0'C air isotherm and implv that the mean annual temperature was depressedapproximately 7 to 8'C during a periglacial episodein the late Wisconsin.A dry continental climate with a seasonaldistribution of precipitation similar to that of the present probably prevailed, and timberline former timberlines. may have been depresseda minimum of 1,240m. The rise in elevation of the rock glaciersfrom east to west acrossthe region is attributed to greater snowfall in west-centralNew Mexico and east-centralArizona, which reducedthe intensity and depth of ground freezing near the late Wisconsin 0"C air isotherm.

Introduction Alsoin thisissue Rock glaciers are periglacial mass-movement deposits that have been described in many alpine areas throughout the world. Wahr- Oil andgas discovery wells of 1993 p.72 haftig (1987) proposed that "rock glacier" be restricted to those formations of blocky debris, extending outward and downslope NMGS1995 spring meeting p.77 moraines of from talus cones or from glaciers or the terminal (1930-1994) p.78 glaciers, that have moved in large part through the deformation RussellE. Clemons of interstitial ice (ice-cemented rock glaciers) or clear ice (ice-cored Statetaxes on naturalresource production p.79 rock glaciers) within them. He also emphasized that masses of blocky debris shown to have accumulated as landslides should NMGS1994 abstracts p. 79 be called a variety of landslide even though they have some mor- Upcominggeologic meetings p. 85 phologic characteristics of rock glaciers. Ice-cemented rock glaciers are cemented by interstitial ice or Service/News p. 86 contain large bodies of solid ice derived either from avalanche p.87 snow or refreezing of melt or spring water (Wahrhaftig and Cox, lndexto Volume16 1959), whereas ice-cored rock glaciers contain cores of massive Stafl notes p. 88 glacial ice (Potter, 1972, p.3027). Ice-cored rock glaciers are characterized by (1) saucer- or spoon-shaped depressions between NMGsubscription information p. 88 the base of the cirque headwalls and the rock glacier heads, (2) longitudinal furrows along both sides, (3) central meandering Gomingsoon furrows, and (4) conical or coalescing pits (White, t976). lce-cemented forms lack depressions at their heads and have contin- Bosquedel Apachehydrogeothermal study and avalanche slopes feeding onto their heads (Luckman uous talus Triassicstratigraphy and chronology and Crocket, 1978).They also are characterized by well-developed Iongitudinal and transverse ridges (White, 1976). central Andes (latitude 33'S) is 1,300 m below the equilibrium marily on t8O variations in ostracodshells. The late Wisconsin line of glaciers on the continental side in Argentina whereas on full-glacial climate between 35,000and 28,600years B.P. was a the maritime side in Chile, they are 700 m below the equilibrium dry and relativelycold period. An abruptwarming eventoccurred line. He ascribes this altitudinal variation to the difference in at28,6ffi yearsB.P., and warm temperaturescontinued until 21,800 climate between the two regions. Greater snow precipitation on years B.P.interrupted by cofd pulsesof short duration. The late the west side of the Andes reduces the intensity and depth of Wisconsinthermal minimum is definedby a cool and wet period freezing and raises the elevation of the lower limit of permafrost. between 21,800and 20,600years B.P. A rapid warming trend at Cort6 (1982b) suggested several regional.factors that promote 20,600 years B.P. marks the close of the late Wisconsin thermal the formation of rock glaciers. Among these are (1) diurnal freez- minimum and was followed by a period of climatic instability ing and thawing, which result in the generation of large volumes characterizedby rapid fluctuations in both temperature and pre- of debris, (2) a mean annual temperature below 0"C, (3) enough cipitation. moisture in the ground to promote cryofraction and gelifluction, (4) moderate to low amounts of precipitation in the form of snow Geographic, geologic, and modern climatic setting for the production of debris and some snow avalanches, and (5) Rock glaciersoccur at seven alpine sites between 33"15'and reduced snow cover that favors ground freezing and cryofraction. 34"15'North latitude in south-centraland west-centralNew Mex- ico and east-centralArizona (Fig. 1). The mountainshave summit Late Wisconsin climate elevationsbetween 2,638 and 3,316m and rise 450 to 1,370m The nature of the late Wisconsin climate in the southwest United above adjacentlowlands. Their slopesare cut by many steep- States has been controversial mainly because of the difference walled canyons with maximum depths of approximately 300 m. between interpretations of the physical evidence and that of the Numerous small canyons and ravines are tributary to the trunk fossil plant record. Models have ranged from climates with lower canyons. winter temperatures to climates with mild winters and cool sum- The rock glaciersin the eastregion are in the Sacramentosection mers, and from climates of decreased precipitation with main- of the Basin and Range province and are formed mainly by fuag- tenance of the present seasonal dishibution to climates with greatly ments of intrusive rocks of mid-Tertiaryage. They are north of increased winter precipitation (Van Devender and Spaulding,7979; the SacramentoMountains, an extensive highland in south-cen- Hawley, 1993). Many of these models were proposed to account tral New Mexico. The rock glaciersin the central and west region for the water budgets of pluvial lakes or were based on the alti- are in the Datil-Mogollon section, a transitional zone between tudinal distribution of cryogenic deposits that are assumed to the Colorado Plateauand the Basinand Rangeprovince that forms indicate lower orographic snow lines and timberlines. Other mod- a large highland in west-centralNew Mexico and east-central els were inferred from fossil plant assemblagesof packrat middens Arizona (Hawley, 1986). They are composed predominantly of and from pollen records of pluvial lakes. debris derived from extrusive rocks of mid-Tertiary age. Galloway (1970) proposed a cold and dry model of late Wis- consin climate in the southwest United States utilizing undated solifluction deposits in the Sacramento Mountains of south-central New Mexico. He postulated a 1,300-1,400-m lowering of tim- New A4exlco berline resulting from a temperature decrease of 10 to 11'C for all seasons and a 10-207o reduction in precipitation. Brakenridge GEOLOGY (1978) also presented evidence for a cold and dry late Wisconsin (full-glacial) climate in the American southwest. He inferred a . Scienceand Service 1,000-m depression of the orographic snowline, timberline, and tssN 0196-948X cryogenic deposits and proposed a 7 to 8'C cooling in all seasons Volume 16, No. 4, Noyember 1994 and no significant increase in annual precipitation. Van Devender et al. (1984) and Van Devender (1990) made Editor: Carol A. Hjellming several inferences about the climate in the Sacramento Mountains Publishedquarterly by in south-central New Mexico during the late Wisconsin (16,000 New Mexico Bureau of Mines and to Mineral Resources 18,000 years B.P.) utilizing macroplant fossils from packrat a division of New Mexico Institute of middens. They suggested that summers were much colder than Mining & Technology today with temperatures probably resembling present tempera- BOARD OF REGENTS tures for late spring or early fall. Winters were not much colder Ex-Officio than today, and most of the precipitation was in winter and spring Bruce King, Gooernorof Nru Meico Alan Morgan, Superintendentof Publiclnstruction with only modest amounts of summer rainfall. Van Devendel and Appointed Spaulding (1979) and Spaulding et al. (1983), using similar data, Diane D. Denish, Prcs.,1992-197, Albuquerque advocated J. Michael Kelly, Sec.lTreas.,1992-1997, RNweU comparable models for an extensive region of the Lt. Gen. Leo Marquez, 7989-1995, Albuquoque southwest United States. SteveTorres, L91-1997, Albuquerque Recent studies in New Mexico present evidence Charles Zimmerly, 1997-7997, Socorro for variable New Mexico Instihrte of Mining & Technology climatic conditions during the late Wisconsin suggesting that all President...... DanielH.L6pez of the models noted above may be, at least, paitially correct. New Merico Bureauof Mines & Mineral Resourc-es Directorand StateGeologisf .. . Charles E. Chapin Phillips et al. (1985)proposed a late Wisconsin climatic model for Sulrciptions: Issued quarterly, Februry May, August, the San Juan Basin in northwest New Mexico utilizing the stable November; subscription price $6.O0/calendaryear. isotopic composition of ground water and noble gaJpaleother- Uitorinl mattet Articles submitted for publication mometry. The period between 24,000 and 21,000 should be in the edito/s hands a minimum of five years B.P. was (5) months before date of publication (February marked by mean annual temperatures 5 to 7"C cooler than present May, August, or November) and should be no longer temperatures resulting in greater effective precipitation. A warm- than 20 typewritten, double-spacedpages. All scientific papers will be reviewed by at least two ing trend began approximately 19,000 years B.P. and coincided people in the appropriate field of study. Address with low effective precipitation. This was terminated by a brief inquiries to Carol A. Hjellming. Editor of Nm Merio episode moist Geology,New Mexico Bureau of Mines & Mineral of conditions approximately 17,000years B.P. The Resources,Smoro. NM 87801{796. latest Wisconsin was characterized by a drier climate with pre- Publishedas publicdomain, therefore reproducible without cipitation no greater than that of the present. Wrmission.Source uedit rcquested. Circulation:1,6ffi - Phillips et aI. (1992) suggested a model of late Wisconsin pa- leohydrologic and paleoclimatic conditions for the San Agusiin P/irterj University o( New Mexico Printing Seilices pluvial-lake basin in west-central New Mexico that is based pri-

November 199,4 New Mexico Geology toa" lo70 106"

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APACH - "ls a ___- l;H"",,;' t lr 010203040 SOCORRO ro -;=: 7 ) lz 0 1020304050km 12 a I SOCORRO ffil Rock glocier site Soutr BatdyEl6 A whir"vt.. Escudilla Mtn. LINCOLN --lnl -__) $'z ORESERVE I ca'izo t"ltn' San Mateo M ts. m cgtlgn Mts' M I ' t. i ['l"ll o CATRON F-{ l4 t-tsl -i 1 2 o si.r,Jlerra ar.n".blanca prl 't0 SIERRA i t- O l. 8 I L.RUIDOSo grn. ls @g36q1on I i t-'- ,__ ( orERo I GRANT RUTH OR CONSEOUENCES tTULlnosl I 33. to8" to70 r06" FIGURE 1-Rock-glacier sitesin south-centraland west-centralNew Mexico and in east-centralArizona. Numbered localitiesidentify weather stations in Tables 2 and 3. Basemaps are the U.S. Geological Survey's base maps of Arizona and New Mexico (scale1:1,000,000).

TABLE 1-Comparative altitudinal and morphological data for the rock-glaciersites in south-central and west-central New Mexico and east-central Arizona.

Highest Average Average peak Number elevation elevation Average Average elevation of rock of fronts of heads length width Site (m) glaciers (m) (m) (m) (n) Capitan Mountains, 3018 76 2430 2538 u7 Lincoln County, New Mexico Carrizo Mountain, 2928 T4 2370 2M7 186 62 Lincoln County, New Mexico Gallinas Peak, 2473 r77 52 Lincoln County, New Mexico South Baldy, 3288 2736 2M 74 Socorro County, New Mexico San Mateo Mountains, 3151 2702 726 u Socorro County, New Mexico Sacaton Mountain, 3249 2891, 2987 203 79 Catron County, New Mexico Escudilla Mountain 3316 12 2935 3030 130 55 Apache County, Arizona

The climate is arid to humid and is controlled largely by alti- of their fronts and heads were determined (Table 1), and the tude. Mean annual precipitation ranges from less than 25 cm extent of vascular plant cover was noted. Aerial photographic along the Rio Grande and in the Tularosa Basin to more than 75 interpretations of the rock glacierson SacatonMountain and Es- cm on mountain summits above 3,050m. Uplands with extensive cudilla Mountain were reported by Blagbrough $99\. Field stud- dreasabove 2,750m often receive more than 50 cm of rainfall per ies were carried out in the Capitan Mountains (Blagbrough, l99la), year. Mean annual temperatures range from 15'C along the Rio Carrizo Mountain (Blagbrough,19&l), GallinasPeak (Blagbrough, Grande and in the Tularosa Basin to near freezing on mountain unpublished data), South Baldy (Blagbrough and Brown, 1983), summits above3,050 m. and the San Mateo Mountains (Blagbrough and Farkas, 1968; Blagbrough, 1986).At these sites, notations were made of size of the debris, soil and vegetation covet slope and height of the Description fronts, and dimensions of the ridges and furrows. One hundred twenty-eight tongue-shapedrock glaciersin the The rock glaciers are at the base of talus at the heads of trunk region were identified on U.S. ForestService aerial photographs canyons and in side canyons and ravines (Blagbrough, 1991b). and plotted on U.S. Geological Survey topographic maps (scale They face in all directions of the compassbut are most common l:24,000). Their lengths, widths, orientations, and the elevations on northwesterly, northerly, and northeasterlyfacing slopes.Their

Nal Mexico Geology November 1994 WEST

CARRIZO CAPITAN SAN MATEO SOUTH ESCUDILLA MTN. MTS BALOY MTN. MTS,

RIO GRANDE

l# Modern timberline

Late Wisconsin orographic snow line Modorn 0' C lsothsrm

ffi Late Wisconsin 0o C isolherm

rock glacle.s tr Altltudlnal llmlts of FIGURE 2-Generalized topographic profile across the region showing rock-glacier occurrences, the elevation of the modern and late Wisconsin 0'C air isotherm, and the late Wisconsin orographic snow line and timberline. Rock-glacier occurrences are determined by the average elevation of the fronts and heads at each site (Table 1). The elevation of the modern 0'C air isotherm is from Table 2. The late Wisconsin 0'C air isotherm is 1,000 m below the modern 0'C air isotherm (P6w6, 1983b). The elevation of the late Wisconsin orographic snow line in the east region is determined by the efevation of the cirque floor on Sierra Blanca Peak (Richmond, 1963) and in the west by the average elevation of the cirque floors in the White Mountains (Melton, 1961). averageelevation rises from east(2,440 m) to west (3,000m) across Moraines of Illinoian agehave broad crests,smooth slopes,and the region (Fig. 2). broadly scattered surface boulders. They bear a mature soil ap- The rock glaciershave steep fronts that slope 20 to 30'and proximately 90 cm thick with a well-developed B horizon. Mo- flanks that rise as steep embankments(Figs. 3 and 4). Heads raines of early Wisconsin age are moderately subdued but merge with talus on the mountain slopes,and central areasslope commonly sharply crested.Their soils are zonal with thicknesses downstream 5 to L5'. On many rock glaciersthe flanks are delin- of 25 to 30 cm. Moraines of late Wisconsin age have irregular eated by lateral ridges that stand higher than central areas and form, abundant surface boulders, and an immature soil 20 to 25 often border depressed areas that extend from the crest of the cm thick. Moraines of Holocene age are blocky and have sharp fronts to the heads. Many lateral ridges bend to form transverse constructional relief. They bear a thin azonal soil where fine ma- ridges at the crest of the fronts, and longitudinal and transverse terial is exposedat the surface. ridges and furrows are common surface features on most rock Soils on the rock glaciers examined in the field suggest that glaciers(Fig. 5). they are equivalent in age to the Holocenemoraines becauseboth Multitongued rock glaciers occur on Carrizo Mountain (Blag- deposits have shallow azonal soils that developed on sediment brough, 1984)and on SanMateo Peak in the SanMateo Mountains between boulders. However, this method of correlation may not (Blagbrough, 1986).They are formed by two talus tongues, the be reliable becauseof altitudinal differences that influenced the upper having overridden the head of the lower. Multilobed tongue- local climate. At the present time the rock glaciers(2,400 to 3,000 shaped rock glaciersare in trunk canyons on the north and south m) exist under a semiarid to subhumid climate, whereas the Ho- sides of the Capitan Mountains (Blagbrough, l99la). They are locene moraines (3,500m) are under a humid climate. Such var- formed by two or more lobes of talus that moved onto the valley iations must have existed in the past and would have had a floors from the side-walls, and manv have surface features in- significant influence on soil development, intensifying the proc- dicating they developed from lobate iock glaciers that coalesced ess at higher elevations becauseof greater precipitation. on the valley floors. In addition, the rock glaciersare composedof coarsetalus with The rock glaciers are composed predominantly of angular to voids between the debris so that some time lag was required in subangular blocks and slabby clasts of fine-grained igneous rock the acquisition of the fines that are necessaryfor soil-building with average diameters between 60 and 90 cm. On most rock- processes.The Holocene moraines probably had fines exposed glacier surfaces, the debris is a jumbled mass with no apparent at the time of deposition that provided an immediate basis for orientation of the blocks and slabby clasts. The debris is stable, soil-building processes.Because the rock glaciers have existed and all but freshly exposed or overturned rock surfacesare oxi- under a more-arid climate than the Holocene moraines, and be- dized and contain a growth of lichen. Some fragments have un- causethey lacked fines at the time of deposition, they are thought dergone frost shattering while on the rock-glacier surface. to have formed during a periglacial episode in the late Wisconsin Soil and vascular plants cover l0 to t\Vo of the rock-glacier when temperatures were lower than those of the present. surfaces. The soil is dark brown and azonal with a maximum In considering the age of rock glaciers it is important to be thickness of approximately 15 cm. It occurs as isolated pockets aware that the climate under which they formed may differ greatly and is formed by decomposedorganic material filling voids be- from that under which they may have moved a little. Rock glaciers tween the blocks and slabby clasts.Trees and shrubs grow in the require a periglacial chmite of sufficient intensity and duration soil and proiect through the debris on some rock glaciers. to generate talus and to mobilize the talus into rock glaciers, whereas the preservation of interstitial ice can take place under a climate with a mean annual temperature of 0" to - 1'C that may Age be either of long or short duration. Soil and vascular plants on The glacial deposits in the Sangrede Cristo Mountains in north rock glaciers probably date from the termination of the last epi- New Mexico, on SierraBlanca Peak in south-centralNew Mexico, sode of significant movement and do not necessarilyindicate the and in the White Mountains in east-centralArizona are used as age of formation. r_eferencefor estimating the age of the rock glaciersin the region The rock glaciers in the region may have formed during the (Merrill and Pdw6,1972,1977; Richmond, L963,7986).In utiliZing cold and dry episode between 35,000and 28,600 years B.P. re- the glacialrecord, it is necessaryto note the lack of firm agecontrol corded in the paleoclimatic model of pluvial-lake San Agustin for the glacial deposits and to point out that climatic conditions (Phillips et al., 1992).Subsequent movement could have taken that favored formation of glaciers may differ greatly from peri- place during the late Wisconsin thermal minimum (24,000to 21,000 glacial conditions that promoted generation of the rock glaiiers. vears B.P.) noted in the climatic records for the San Tuan Basin

November 1994 New Mexico Geology FIGURE 3-Low-angle aerial photograph of the two large rock glaciers in the east and west branches of Corral Canyon on the north side of the Capitan Mountains The view is to the south and shows the steep fronts and flanks and the longitudinal and transverse ridges and furrows. The scarcity of soil and vegetation on the rock glaciers suggests movement near the close of the late Wisconsin

and pluvial-lake San Agustin (Phillips et al.,1986, 1992). Rock- glacier creep during a periglacial episode near the close of the late Wisconsin would account for the sharp constructional relief and restrictive development of soil on the rock glaciers. FIGURE 4-Low-angle aerial photograph of the large rock glacier in the east branch of Ferris Canyon on the north side of the Capitan Mountains. The view rock glacier has a steepfront and flanks, Paleoclimatic inferences is to the southeist. The with lateral ridges along the flanks that bend to form a transverse ridge The rock glaciers in the region are thought to have moved by at the crest of the front. Two smaller rock glaciers in the foreground extend the flow of interstitial ice (permafrost) because they have contin- from the west wall of the canvon onto the floor.

Present-day precipitation in the San Mateo Mountains is sufficient for the formation of interstitial ice (Blagbrou gh, 7986;Blag- brough and Farkas, 1968), and climatic data for the Capitan Mountains indicate that mean temperatures for the winter months

Within the zones the mean annual temperature was below freezing and the snow cover was thin and of short duration. Prolonged periods of diurnal freezing and thawing resulted in intense freJze- that generated large volumes of talus in favorable [li#,f."." The modern mean annual temperature at the average elevation of the rock glacier fronts and the modern 0"C air isotherm are computed for the rock-glacier sites in Table 2 using a lapse rate of 0.72"C1fi0 m, established by Van Devender et al. (1984) in FIGURE S-Low-angle aerial photograph of the rock glacier in the west south-central New Mexico, and climatic data from the nearest branch of Ferris Canyon on the north side of the Capitan Mountains weather stations maintaining long-term weather records. The late View is to the south. The rock glacier has a steep front approximately 75 m high, Wisconsin 0"C air isotherm is 1,000 m below the modern 0"C air Iateral ridges along the flanks, and longitudinal and transverse ridges and furrows on the surface. isotherm (P6w6, 1983b, p. 175). The lower limit of rock-glacier activity in the east region closely approximates the late Wisionsin 0"C air isotherm, whereas in the west region the lower limit of rock-glacier activity is approximately 460 lo 590 m above the 0'C This amount of lowering may approximate the actual depression air isotherm (Fig. 2). because the lower limit of rock-glacier activity nearly coincides The modern mean annual temperature at the average elevation with the late Wisconsin 0'C air isotherm. The inferred reduction of the rock-glacier fronts in the east region is 7.2 b 7:.9'C, which in the mean annual temperature conforms to that proposed by implies that the mean annual temperature was depressed a min- Brakenridge (1978), is less severe than that advocated by Galloway imum of approximately 7 to 8'C in south-central New Mexico (1970), and is marginally higher than that inferred by Phillips et during one or more periglacial episodes of the late Wisconsin. al. (1986). ir?

New Mexico Ceology November 1994 TABLE 2-Mean annual temperatures at the average elevation of the rock-glacier fronts and the elevation of the rnodern and late Wisconsin 0"C air isotherm at the rock-glacier sites in south-central and west-central New Mexico and east-central Arizona. Weather stations are in Fig. 1. Climatic data is from Gabin and Lesperance (1977), Kunkel (1984), and Sellers and Hlll (7974).

Mean Average annual Elevation elevation Elevation Mean temp. modern rock-glacier weather Years annual rock-glacier 0'C air fronts Weather MaP station of temp. fronts isotherm Site (m) station locality (m) record fc) fC) (rn)

Capitan Mountains 2430 Fort Stanton 2 7826 74 11.1 t.J J+J/ Carrizo Mountain 2370 Carrizozo A 1658 58 12.3 7.2 3360 Gallinas Peak 2413 Corona 5 2026 47 70.7 3572

South Baldy 2736 Magdalena 7 1994 JO 11.1 5.8 3536 San Mateo Mountains 2702 Winston 8 1890 35 17.4 6.7 3473 SacatonMountain 2897 Glenwood 9 7MT 36 74.3 3.7 3427 Escudilla Mountain 2935 Alpine 11 2454 27 6.4 2.9 3343

The modern timberline occursat an elevation of approximately The rise in altitude of the rock glaciersfrom east to west across 3,640 mjust north of SierraBlanca Peak in the SacramentoMoun- the region may be due to more-abundant snow fall in the west tains (Dyer and Moir, 1977) approximately 1.,240m above the region during the late Wisconsin. Table 3 demonstrates that a lower limit of rock-glacier activity in south-central New Mexico. greater percentageof the total mean annual precipitation occurs This suggests that timberline was lowered a minimum of 1,240 during the winter months of December,|anuary, and February m in the locality during the late Wisconsin. This amount of de- at weather stations in west-central New Mexico and east-central pression is somewhat lessthan that proposed by Galloway (1970), Arizona than at those in south-central New Mexico. This can be is substantially greater than that inferred by Brakenridge (1978), attributed to the location of the west region nearer to the Pacific and is far in excessof the vegetation lowering recorded in the Ocean, which is the principal source of winter moisture in the packat midden records of the northern Chihuahuan Desert (Van southwest United States. Devender, 1990). MiddleJatitude Pacific-type winter storms probably were in- The lower limit of rock-glacier activity in the east region is tensified and displaced southward during the late Wisconsin approximately 1,100m below the late Wisconsin orographia snow (Spauldinget al., 1983).This would have enhancedwinter pre- line on Sierra Blanca Peak (Fig. 2). In comparison, most active cipitation in the west region and may be responsiblefor the lower rock glaciersoccur near the orographic snow line, many in cirques altitude of the orographic snow line in the White Mountains (3,260 (Flint, 1971, p. 273). This is demonstrated by the lower limit of m) as compared to that on Sierra Blanca Peak (3,400m). Greater active rock glaciersin the Swiss Alps approximately 400 m below snow precipitation on SacatonMountain and EscudillaMountain the present snow line (Barsch, I969a, 1969b)and by the same apparently reduced the intensity and depth of ground freezing limit in the Alaska Range approximately 120-360 m below the near the 0'C air isotherm and raised the lower level of permafrost present snow line (Wahrhaftig and Cox, 1959).These occurrences approimately 570 m above the 0'C air isotherm. appear to indicate a significant difference between the Late Wis- AcrNowrroGEMENTS-The author wishes to expresshis appre- consin periglacial climate in south-central New Mexico and the ciation to |. W. Hawley, D. W. Love, T. L. P6w€,and S. E. White present periglacial climate in mountain rangesat higher latitudes. for their critical reviews of this paper and suggestions for its Barsch and Updike (1971) suggested that such variations in improvement. Appreciation also is extended to Michdle Brand- altitude may be due to the more intense radiation and the greater wein and FrancisVarney for their help in editing the manuscript. aridity in the southwest United States.They noted that both factors have a greaterimpact on glaciersthan on rock glaciersbecause the interstitial ice is protected from direct radiation and subli- References mation bv the blockv mantle of debris. Barsch,D., 1969a,Permafrost in der oberensubnivalen stufe der Alpen: Geographica Aridity in the Helvetica,v.24, pp. 70-1.2. southwest United States is also important in Barsch, D., 1969b,Studien und messungen an blockgletschernin Macun, Unter- determining the lower limit of rock glaciers becauseit restricts engadine: Zeitschrift fiir Geomorphologie, Supplementband, v 8, pp. 11-30. snow fall. Marker (1990)noted that periglacial forms tend to ap- Barsch,D., and Updike, R. G., 1971,,Late Pleistocenegeomorphology (rock glaciers pear at lower elevations in the isolated mountains of south New and blockfields) at Kendrick Peak, northern Arizona: Arizona GeologicalSociety, Mexico than in the Sangre de Cristo Mountains in north New Digest, v. 9, pp.225-243. Blagbrough, J. W., 7984,Fossil rock glacierson Canizo Mountain, Lincoln County, Mexico and in the Front Range in Colorado. She attributed this New Mexico: New Mexico Geology, v. 6, pp. 55-68. to the aridity in south New Mexico that reduces winter snow Blagbrough, J. W., 1985,A fossil rock glacier on San Mateo Peak, SocorroCounty, cover and lowers the timberline exposing lower altitudes to peri- New Mexico: New Mexico GeologicalSociety, Guidebook to 37th Field Conference, glacial processes.Such conditions could have been enhanceddur- pp.101-105. Blagbrough, J. W.,1991a, Late Pleistocenerock glaciersin the western part of the ing the late Wisconsin resulting in permafrost and intense frost Capitan Mountains, Lincoln County, New Mexico: description, age, and climatic action occurring at lower altitudes in the isolated mountains in significance:New Mexico CeologicalSociety, Guidebook to 42nd Field Conference, the south than in the larger mountain massesfarther north. pp. 333-338. The observations Blagbrough, J. W., 7997b,Paleoclimatic significance of rock glaciersin south-central noted above suggestthat the rock glaciersin and west-centralNew Mexico: GeologicalSociety of America, Abstractswith Pro- the east region formed under a cold and dry continental climate grams,v. 23, no.4, p. 5. that resulted in a thin snow cover of short duration. This favored Blagbrough, t. W., 1994, Photointerpretation of ancient rock glaciers on Sacaton the formation of permafrost and intense freeze-thaw action near Mountain and Escudilla Mountain, Datil-Mogollon upland, west-cenhal New the 0"C air isotherm Mexico and east-centralArizona: New Mexico GeologicalSociety, Guidebook to and resulted in a lower limit of rock-glacier 45th Field Conference, pp. 315-321.. activity approximately 7,1,00m below the orographic snow line. Bfagbrough,J. W, and Brown, H. G.,1lI, 1983,Rock glacierson the west slope of The mean annual precipitation and the seasonaldistribution of South Baldy, Magdalena Mountains, Socorro County, New Mexico: New Mexico precipitation may have approximated that of the present with a Geological Society,Guidebook to 34th Field Conference,pp.299-302. summer maimum because increased precipitation during the Blagbrough,J. W., and Farkas,S. E., 1968,Rock glaciers in the SanMateo Mountains, south-centralNew Mexico: American Journal of Science,v. 266, pp. 812-823- winter months would have resulted in a more permanent snow Brakenridge,G. R., 1978,Evidence for a cold, dry full-glacialclimate in the American cover that restricted periglacial processes. Southwest: Quaternary Reseatch,v. 9, pp. 22-40.

November 1994 New Mexico Geology TABLE 3-Mean annual precipitation and winter precipitation (December,fanuary, and February) at selectedweather stations in south-central and west-central New Mexico andiast-central Arizona. Weither staiions are in irig. l. tlimatic data ii from Gabin and Lesperance(1977)' Ktnkel (79M)' and Sellers and Hill (1974).

Precipitation (cm) Years MaP Elevation of Mean Percentage Station Location locality (m) record annual Winter in winter Arabella Lincoln County, 7634 17 5.23 10.0 New Mexico

Fort Stanton Lincoln County, t896 +J 35.51 4.56 72.8 New Mexico Capitan Lincoln County, I97L A' 39.60 J.UJ 72.7 New Mexico Catrizozo Lincoln County, 1658 53 33.87 5.36 15.8 New Mexico Corona Lincoln County, 2026 46 38.48 5.49 New Mexico Kelly Ranch Socorro County, 2043 39 36.10 4.47 72.2 New Mexico Magdalena Socorro County, L994 53 28.82 3.59 72.5 New Mexico Winston Sierra County, 1890 35 3.08 9.8 New Mexico Glenwood Catron County, 1M7 36 37.95 9.27 24.3 New Mexico Mogollon B Catron County, 10 2072 13 46.92 11.18 23.8 New Mexico Alpine Apache County, l1 2451, 30 49.56 IU.JJ 20.8 Arizona Greer Apache County, t2 2591 20 67.54 76.54 26.9 Arizona

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Na p Mexico Geolo3y November 1994