Great Basin Naturalist
Volume 54 Number 2 Article 6
4-29-1994
Full-glacial shoreline vegetation during the maximum highstand at Owens Lake, California
Peter A. Koehler Northern Arizona University, Flagstaff, Arizona
R. Scott Anderson Northern Arizona University, Flagstaff, Arizona
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Recommended Citation Koehler, Peter A. and Anderson, R. Scott (1994) "Full-glacial shoreline vegetation during the maximum highstand at Owens Lake, California," Great Basin Naturalist: Vol. 54 : No. 2 , Article 6. Available at: https://scholarsarchive.byu.edu/gbn/vol54/iss2/6
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FULL-GLACIAL SHORELINE VEGETATION DURING THE MAXIMUM HIGHSTAND AT OWENS LAKE, CALIFORNIA
Peter A. Koehlerl and R. Scott Anderson1,2
ABSTRACT.~Owens Valley, California, was markedly different during the Wisconsin glacial stage from what it is today. Alpine glaciers bounded the Sierra Nevada, and pluvial Owens Lake reached highstands and overflowed its nat ural basin. We analyzed three layers from two packrat middens, dated to ca 23,000-14,500 yr BP, obtained from Haystack Mountain (1155 m) only 10 m above and <100 ill from the highstand strandline ofpluvial Owens Lake. Dur ing this period vegetation near Owens Lake reflects the influence ofthe Tioga glacial advance and retreat on lake levels, and microclimatic effects on shoreline vegetation. Between ca 23,000 and 17,500 yr BP a Utah juniper (Juniperus osteospenna) and single-needle pinyon pine (Pinus monophylla) woodland existed at the site. In the layers dated to ca 17,500 and 16,000 yr HP, macrofossils document the presence of Rocky Mountain juniper (juniperus scopulorum), a species that no longer occurs in California. It is suggested that meltwater from the retreating glacial ice inundated the Owens River Lake chain causing pluvial Owens Lake to reach its highstand. This caused an increase in effective mois ture, due to high groundwater, allowing the mesophytic Rocky Mountain juniper to exist at the site.
Key words: paleoecology, packrat middens, Rocky Mountain juniper, Juniperus scopulorum, pluvial Owens Lake, Tioga glacial stage, California.
Few places in western North America The goal ofthis study was to investigate the record such a full range of Quaternary events pleni- to late-glacial vegetation communities as found in the Owens Valley of eastern Cali near pluvial Owens Lake (Fig. 1), which fluc fornia, Within the confines of the narrow tuated considerably during this period. Owens River corridor, never more than 33 km Increased effective moisture and glacial runoff wide, is found evidence of late-Quaternary during the late "Tisconsin initiated a series of glacier expansions (Birkeland and Burke 1988, overflow events in the lakes that define the Bursik and Gillespie 1993), volcanic eruptions Owens River system (Fig. 1). The chain began (Pakiser et aJ. 1964), and expansion and con in the Mono Lake Basin where Pleistocene traction of large "pluvial" lakes (Lajoie 1968, Lake Russell (Putnam 1950) overflowed when Smith and Street-Perrott 1983, Benson et aI. it filled to 2175 m elevation (Lajoie 1968, Ben 1990). Such deposits are the manifestations of son et aJ. 1990). Owens River then flowed great climatic and environmental changes that through the Adobe Valley and mixed with have occurred during the late Quaternary. waters from Long Valley en route to Owens Less studied but equally striking is the Lake. Owens Lake periodically filled and record ofhiological changes contemporaneous overflowed at 1145 m. Eventually, runoff and associated with pervasive changes in the flowed to China and Searles lakes, then into physical system. Pollen from pluvial lake sedi Lake Manly in Death Valley (Smith and ments (Leopold 1967, Batchelder 1970, Davis Street-Perrott 1983). Lake levels fluctuated unpublished) has been used to reconstruct the considerably between ca 24,000 and 21,000 yr broadscale, regional changes in vegetation. Bp, followed by high and relatively stable lake Other studies (Koehler and Anderson 1990, levels between 21,000 and 14,000 yr BP Jennings and Elliott-Fisk 1993, Koehler (Smith and Street-Perrott 1983). unpublished) have relied on packrat (Neotoma) Six layers from two packrat middens found middens, which record local vegetation at 1155 m elevation in Owens Valley, Inyo changes. A combination of all proxy indicators County, California (Fig. 1), document full will ultimately allow a comprehensive picture glacial vegetation changes during the period ofenvironmental change to be revealed. hetween ca 23,000 and 14,500 yr BP. The
lQuaternary Studies Program, NorthclTI Ariwna University, Flagstaff. Arizona BOOll. 2Environmenlal Sciences Pro~ram, North.ern Arizona University. Flagstaff. Arimml 86011,
142 1994] SHORELINE VEGETATION DURING H,GHSTAND 143
".. 121'" ".. .,' -r;:::==:::::J'===;---::j =-.. l.ogend '"6 ...... ~ P1eislocena tNet pdrw.W'S +3385m 1,;:::,1 P18l1tl08l'1t lakes "" 6 Pactua micifen locItions -
•• - Salol>co..awy + Clher loaiions • r..... ,~ t.blntain O't!l \ 38"
klarnrtirt o f I "..
I
35'
o 200 I----;c;;::':' kilometers=---, "" "7' Fig. 1. Map showing the Owens Lake chain and sites discussed in the text (map is after Smith and Street-Perrott 1983).
midden assemblages described here are impor gests that pluvial highstands during glacial tant in deducing paleoenvironments of the retreats produced a unique microclimate at region for several reasons. First, the middens this nearshore location. occur within 10 m elevation of and < 100 m away from the pluvial Owens Lake maximum THE SITE highstand strandline. Second, the occurrence within several middens ofplant macrofossils of Owens Valley lies between the massive Rocky Mountain juniper !juniperus scop,Jo Sierra Nevada to the west and the Inyo-White rum), a tree not found today in California, sug- Mountain rolIlges to the east The Sierra Nevada 144 GREAT BASIN NATURALIST [Volume 54 rise from California's Great Valley, with a gen (llOO m, 16 km soutlleast of the site), record tle westward gradient of 6% toward a lofty an annual precipitation of 127 mm/yr and 80 crest that contains some 500 summits over mm/yr (Lee 1912, Elford 1970), respectively. 3660 m, with 11 peaks over 4260 m. The east Precipitation occurs primarily in the winter ern escarpment ofthe Sierra plummets, with a months with some rainfall in the summer ca 14% gradient, as much as 3050 m into the months as isolated thunderstorms. Precipita Owens Valley. The graben forming Owens Val tion of 203-304 mm/yr has been estimated for ley ranges ca 13-33 km wide, with an average the pinyon woodlands ofthe White Mountains elevation of only 1160 m. The eastern flank of at elevations of1525-2135 m (St. Andre 1965). the Owens Valley is bounded by the Inyo White Mountain chain, with a crest elevation METHODS that averages ca 2900 m. Two indurated packrat middens, containing Three layers (A-C) were found in each of six stratigraphic units, were found at a single the two middens (lIMI and lIM2) and were location on Haystack Mountain, ea 3 km east separated along stratigraphic planes. Once of the Inyo Mountains (36°36'N, 118°05'W; separated, the samples were disaggregated in Fig. 1). The outcrop where the middens were distilled water in a covered bucket. This was found is of a spheroidally weathered Creta done to prevent contamination by modern ceous granite (Ross 1967) and faces southeast. pollen. The disaggregated middens were At 1155 m the site is located ca 100 m north sieved through a number 20-mesh (0.85-mm) and 10 m above the Owens Lake highstand screen ",rith the decant saved for pollen analysis. strandline (ll45 m). The midden debris was air-dried and hand Currently the local vegetation is dominated sorted nnder a dissecting microscope (7-40X by a saltbush (Atriplex spp.)/hopsage (Grayia magnification). Plant macrofossils were identi spinosa)/sagebrush (Artemisia spp.) communi fied from reference materials. Interpretation ty on the valley floor, wbile wolfberry (Lycium of the macroremains is based on a relative andersonii), mallow (Sphaeralcea spp.), and abundance scale with 5 = > 200 macrore various species of the grass family occupy the maius, 4 = 100-200, 3 = 30-99, 2 = 2-29, immediate rock outcrop. Creosote bush (Lar and a single specimen = 1 (Van Devender et rea /ridentata) and bursage (Ambrosia dumosa) al. 1987). Radiocarbon data were obtained pri are found locally on well-drained sites, and marily on fecal pellets (Table 1). greasewood (Sarcobatus vermiculatus) occurs Processing for fossil pollen followed Faegri on sites with alkaline soils and high water and Iverson (1989) and included the addition tables. of Lycopodium tracer tables (Stockman 1971), Vegetation that occurs from 1150 m on the acetolysis, staining, and suspension in silicon alluvial fans to 1950 m is represented by a oil. A 300-grain count (range = 262-361; Mojave Desert community dominated by cre Table 3) ofterrestrial pollen types was made at osote bush and bursage. Joshua tree (Yucca 400X magnification. The count excluded tracer, brevifolia), single-needle pinyon pine (Pinlh' deteriorated, and aqnatic pollen types. Pollen monophylla), and spiny menodora (Menodora percentages were calculated based on the spinescens) occur in a transition zone (1950 total terrestrial pollen counted in each sample. 2100 m) that trends into a pinyon-Utab Many of the pollen types were identified to jnniper !Juniperus osteosperma) woodland at ca 2100-2900 m. In the southern Inyo Moun tains subalpine trees are found only on peaks TABLE L Radiocarbon analysis of the Owens Lake site above ca 2900 m. Limber pine (Pinus flexilis) (1155 m), Inyo County, California. is common in this region, with lesser amounts Sample Radiocm'bon Dated Lab of bristlecone pine (Pinus longaeva), fernbush years B.P. material number (Chamaebatiaria millefollium), and sagebrush. HM2A 14,870 + 130 Dung Beta-39274 Several individuals of Sierra juniper (junipe HM2C 16.010 + 330 Dung Beta-36732 rus occidentalis var. australis) also grow in the HM2B 17,680 + 150 Dung Beta-35503 Inyo Mountains (Vasek 1966). HMIA 20,590 + 210 Debris Bcta-40000 HMIB 20,960 ± 240 Dung Beta-34833 The nearest weather stations, Lone Pine HMIC 22,900 + 270 Dung Beta-39273 (1l20 m, 8 km west of the site) and Keeler 1994] SHOHELINE VEGETATION DURING HIGHSTAND 145 family; however, some types were broken into lation ofcosmogenic CI-36 suggests that maxi morphological categories. Pinus pollen was mum Tioga glaciation occurred prior to ca separated into the haploxylon (white pine) and 21,000 yr BP (Phillips et al. 1990). Radiocar diploxylon (yellow pine) groups. Ephedra bon dates of 21,000 + 130 yr BP (Lebetkin pollen was divided into E. viridis and E. cali 1980) from tufa underlyiug an alluvial fan of fornica pollen types. Purshia-Cercocarpus inferred Tioga-age at Owens Lake (Fullerton pollen types were discriminated from 1986) and of 19,050 ± 210 yr BP on basal rock Rosaceae, and Sarcobatus was separated from varnish from an outermost Tioga moraine in other members of the Chenopodiaceae-Ama Pine Creek (Dorn et al. 1987) also support a ranthus (Cheno-am) group. maximum advance before this time. Timing on Sierra Nevada deglaciation is recorded by RESULTS dates of glaciolacustrine sediments from mid elevation west-side lakes (Swamp Lake ca Macrofossils recovered from the middens 15,565 yr BP [1957 m; Batchelder 1980], Lake document plants typically found in the pin Moran ca 14,750 yr BP [2018 m; Edlund and yon-juniper zone of the Iuya Mountains. The Byrne 1991], Swamp Lake Yosemite ca 13,350 exception to this is the occurrence of Rocky yr BP [1554 m; Smith and Anderson 1992]) Mountain juniper (juniperus scopulorum), and rock varnish dates on recessional Tioga which does not occur today in California. Fos moraines of ca 13,910 yr BP from Pine Creek sil pollen recovered from the middens repre (1830 m; Dorn et al. 1987). Dates from near sents plants found within the midden as well the Sierran crest at Barrett Lake (2816 m) of as local species that either are avoided by ca 12,500 yr BP (Anderson 1990) and ca packrats or occur beyond their foraging range 10,300 yr BP in the Cottonwood Basin (ca (Anderson and Van Devender 1991). 3000 m elevation; Mezger 1986) document Midden macrofossils are represented by high-elevation deglaciation on the east side. the presence of Utah juniper in all samples The presence of ice in the Sierra Nevada (Table 2). Green ephedra (Ephedra viridis), had a significant impact on paleoenvironments wild rose (Rosa woodsii), Merwdora, and pin within Owens Valley. The Owens River water yon pine occur in most of the other samples. 2 Nevada greasebush (Forsellesia nevadensis) shed covers ca 8500 km , with nearly all of its runoff originating in the 16% of this area lying and Joshua tree also occur in several of the older middens (ca 22,900-20,590 yr BP). in the eastern Sierra Nevada (Lee 1912, Smith Rocky Mountain juniper is present in two and Street-Perrott 1983). Thus, as melting middens dated to ca 17,680 and 16,010 yr BP. glaciers retreated, lakes within the valley Pollen identified from the middens gener would periodically fill, overflowing to a down ally supports macrofossil evidence (Table ,3). stream lake in the chain. Based on glacial fea Exceptions to this are the high amounts of tures, the glacial ice west of the Sierra Nevada Artemisia (ca 6-50%) and moderate amounts crest increased the average elevation by ca 50 of Cheno-ams (ca 5.5-18%). High variability m in the south (Gillespie 1982, Mezger 1986) within pollen percentages may be due to the to as much as 300 m in the Yosemite National uncertain association with deposition time Park area (Alpha et al. 1987). Elevational in (months to centuries) and the year-to-year creases east of the crest were insignificant variability in pollen production. because their glaciers were largely restricted to steep valleys. During the period of maxi DISCUSSION mum ice extent within the Sierra Nevada, the increased average elevation of the range, During the Pleistocene several alpine glac caused by the combination of upwards of ca ier advances sculpted the Sierra Nevada, with 600 m ofice plus the ca 100 m lowering of sea at least three stages recorded during the late levels, may have had two effects on the Owens Wisconsin (Bursik and Gillespie 1993). The Valley and 1nyo-White Mountains to the east. most recent episode, the Tioga advance, First, the higher average elevation of the Sier occurred during the full-glacial period, ca ra Nevada intensified the rainshadow effect, 21,000-18,000 yr BP. SigniHcant advauces in as witnessed by the limited glaciation within glacial chronology have been made in the last the 1nyo-White Mouutains (Elliott-Fisk 1985, decade. Experimental analysis of the accumu- Swanson et al. 1993). Second, accumulation of 146 GREAT BASIN NATURALIST [Volume 54
TABLE 2. Plant macrofossils identified from the Owens Lake site (1155 m), Ioya County, California. Relative abun- dance is based on >200 specimens = 5, 100-200 = 4, 30-99 = 3, 2-29 = 2, and a single specimen = 1. Sample unit HM2A HM2C HM2B HMIA HMIB HMIC Sample age yr B.P. 14,870 16,010 17,680 20,590 20,960 22,900
TREES/SHRUBS Juniperus osteosperma 4 4 4 3 5 5 Juniperus scopulorum 3 2 Pinus monophylla 2 2 3 2 Ephedra viridis 2 2 5 5 5 Menodora spinescens 2 2 2 2 Mirabilis bigelovii 2 2 3 Eriogonum cf. fasiculatum 2 Forsellesia nevadensis 3 2 5 Artemisia tridentata 1 Chrysothamnus teretifolius 2 2 2 2 2 Ericameria cuneata 2 2 2 2 2 2 Tetradymia sp. 2 Atriplex polycarpa 1 Atriplex confertifolia 1 Grayia spinosa 1 Rosa woodii 2 2 2 2 Coleogyne ramosissima 1 Yucca cf. brevifalia 2 HERBS Sphaeralcea amhigua 2 2 2 Cirsium sp. 2 1 2 Boraginaceae 2 Amsinkia sp. 2 Cryptantha sp. 2 Plagyhothrys spp. 2 Salvia sp. 1 Orthocarpus sp. 2 SUCCULENT Opuntia basilaris 1 2 2 4 4 GRASS Oryzopsis hymenoides 2 2 2 ice in the central Sierra Nevada probably intermediate levels from at least 35,000 yr BP deflected storm tracks further south than until a highstand after 15,000 (ca 14,000 or today and at a more frequent rate, as wit 13,000 yr BP; Benson et al. 1990), nessed by wetter conditions in the modern During the full-glacial, the Owens Lake Mojave Desert at that time (Spaulding and midden site was located in a transitional posi Graumlich 1986). tion between the full-glacial single-needle While the lake-level fluctuations at Owens pinyon-juniper woodlands of the Mojave Lake are poorly known, the periods of high Desert and the Utah juniper-limber pine stands and overflow can be estimated from the woodland of the southern Great Basin, lu the detailed records of pluvial Lake Russell and rain shadow of the Sierra Nevada, the Eleana Searles Lake (Smith and Street-Perrott 1983, Range (1810 m) records limber pine and Benson et al. 1990). Owens Lake either steppe shrubs (Spaulding 1990). North of the received overflow from (Lake Russell) or con Owens Lake site at slightly higher elevations, tributed to (Searles Lake) pluvial lakes. Lake colder conditions are recorded by the occur levels at Searles were generally high to over rence of Utah juniper and sparse limber pine flowing between ca 25,000 and 10,000 yr BP. at Eureka View (1430 m) at ca 14,700 yr BP Between ca 21,000 and 15,000 yr BP a contin (Spaulding 1990) and Utah juniper and Great uous highstand is inferred. Lake levels then Basin desert shrubs at the Volcanic Tablelands returned to moderately low levels after ca (Jennings and Elliott-Fisk 1993), Pinyon pine 15,000 yr BP (Smith and Street-Perrott 1983) was not found in Death Valley where Utah or ca 14,000 yr BP (Benson et al. 1990), For juniper existed with a yucca semidesert (260 Lake Russell, lake-level chronologies suggest 1280 m; Wells and Woodcock 1985), South of 1994] SHORELINE VEGETATION DURING HIGHSTAND 147
TABLE 3. Percentages ofidentified pollen types from the Owens Lakes site (1155 m), Inyo County, Califomia Sample unit HM2A HM2C HM2B HMlA HMIB HMIC Sample age yr B.P. 14,870 16,010 17,680 20,590 20,960 22,900 T AQUATICS Typila 0.0 0.0 0.0 0.0 1.0 0.0 the Owens Lake site, the Mojave Desert full Mountain juniper is well understood in the glacial vegetation records the widespread southeastern and central Great Basin (Thomp occurrence of a pinyon-juniper woodland son 1990). Using terpene variations, Adams (Spaulding 1990). (1983) provided evidence for Rocky Mountain Records from the Owens Lake site (U55 juniper colonization in post-glacial environ· m) and Skeleton Hills (925 m; Spaulding 1990) ments within the extreme northern and south are the only documentation of pinyon pine ern extensions of its range, suggesting migra during the full-glacial at this latitude. The tion routes along pluvial lake corridors. Rocky lower limit of pinyon pine is recorded iu the Mountain juniper is generally restricted to Skeleton Hills at 925 m. In Owens Valley the regions that Jack pronounced summer upper limit of pioyon is constrained between droughts (West et aI. 1978, Thompson 1988). 1155 m (this report) and 50 km north in the In the southern part of its range, Rncky Volcanic Tablelands at 1340 m Gennings and Mountain juniper is restricted to riparian set Elliott-Fisk 1993). Despite the absence of tings or areas of shallow groundwater and pinyon at Death Valley, these sites define the springs (Adams 1983). This information is ger northern distribution of pinyon in the Mojave mane to the history of lake-level fluctuations Desert during the fuJI-glacial. within the Owens Valley area. The most interesting macrofossil found in The occurrence of Rocky Mountain juniper the midden series dating 17,680 and 16,010 yr at the Owens Lake site is thus partially ex· BP is Rocky Mountain juniper. 'This tree is not plained by local climatic mctors associated with found in California today but occurs in the pluvialla! JEl\NINCS, S. A., ,\.'10 D. L. ELllOTI-FtSK. 1993. Packrat SPAULDING, W. G. 1981. The late Quaternary vegetation midden evidence of late Quaternary vegetation of a southern Nevada mountain range. Unpublished change in the White Mountains, Califomia- .evada. doctoral dissertation. University ofArizona, Tucson. Quaternary Research 39: 214-22l. _-:c' 1990. Vegetational and climatic development of KOEHLER, P. A., A."'lD R. S. ANDERSON. 1990. Abstract: the Mojave Desert: the last glacial maximum to the Late Wisconsin to recent vegetation changes from present. Pages 166-199 in. J. L. Betancourt, T. R. the Alabama Hills. Owens Valley, California. San Van Devender. and P. S. Martin, eds., Pachat mid Bernardino County Museum Association QUaJterly dens. The last 4.0,000 years ofbiotic change. Univer 36. sity ofArizona Press, Tucson. LAJOIE, K. R. 1968. Quaternary stratigraphy and geologic SPAULDlNG, W. G., AND L. J. GRAUMLICH. 1986. The last history of Mono Basin, eastern California. Unpub pluvial climatic episodes in the deserts of southwest lished doctoral dissertation, University of California, ern North America. Nature 320: 441-444. Berkeley. ST. ANDRE, G. L. 1965. The pinyon woodland zone io the LEBETKIN, L. K. 1980. Late Quaternary activity along the White Mountains of California. American Midland Lone Pine fault, Owens Valley fault zone, California. Naturalist 73: 257-239. Unpublished master's thesis. Stanford University, STOCKMARR, J. 1971. Tablets with spores used in absolute Palo Alto, California. pollen analysis. Pollen et Spores 13; 615-621. LEE, C. H. 1912. An intensive study ofthe water resources SWANSON, T. W., D. L. ELLIOTT'FISK, AND R. S. of a part of Owens Valley, California. USGS Water SOUTHARD. 1993. Soil development parameters in Supply PapeT 124. the absence ofa chronosequence in a glaciated basin LEOPOLD, E. B. 1967. Summary of palynological data ofthe White Mountains, California-Nevada. Quater from Searles Lake. Pages 52--66 in Pleistocene geol nary Research 39: 186-200. ogy and palynology, Searles Lake Valley, California. THOMPSON. R. S. 1988. Vegetation dynamics in the west Friends ofthe Pleistocene guidebook. ern United States: modes of response to climate MEZCER, E. B. 1986. Pleistocene glaciation of Cotton fluctuations. In: B. Huntley and T. Webb HI, eds., wood Basin, southeast Sierra Nevada, California. Vegetation history. Kluwer Academic Publishers. Unpublished master's thesis, University of Southem _--c' 1990. Late Quaternary vegetation and climate in California. the G.·eal Basin. Pages 200--239 in J. L. Betancourt, PAX.ISER, L. C., M. F. KANE, AND W. H. JACKSOK. 1964. T. R. Van Devender. and P. S. Martin, cds., Pachal Structural geology and volcanism of Owens Valley middens. The last 40,000 years of biotic change. region, California-a geophysical study. USGS PTO University ofArizona Press, Tucson. fessional Paper 348. VAN DEVENDER, T. R.. R. S. THOMPSON. AND J. L. BETAN~ PHILLIPS, F. M., M. G. ZREDA, S. S. SMITH, D. ELMORE, COURT. 1987. Vegetation history in the southwest; P. W. KUBIK, AND P. SHARMA. 1990. Cosmogenic the nature and timing of the late Wisconsin chlorine-36 chronology fOT glacial deposits at Bloody Holocene transition. Pages 323--352 in W. F. Ruddi~ Canyon, eastern Sierra Nevada. Science 248: man and H. E. Wright, Jr., eds., North America and 1529-1532. adjacent oceans during the last deglaciation. eSA, PUTNA~f, W. C. 1950. Moraine and shoreline relationships Boulder. at Mono Lake, California. Geological Society of VASEK. F. C. 1966. The distribution and taxonomy of America Bulletin 61: 115-]22. three western junipers. Brittionia 18; 350-372. Ross, D. C. 1967. Generalized geologic map of the lnyo WELLS, P. V., AND D. WOOOCOCK. 1985. Full.g1acial veg Mountains region, California. USGS Miscellaneous etation of Death Valley, California: juniper wood Geologic Investigations Map 1-506. land opening to yucca semidesert. Madrono 32: SMITH. G. I., AND F. A. STREET-PERROTI. 1983. Pluvial 11-23. lakes ofthe western United States. Pages 190-212 in WEST, N. E., R. J. TAUSCH, K. H. REA, AND P. TUELLER. S. C. Porter, ed., Late Quaternary of the United 1978. Phytogeographical variation within juniper· States. University of Minnesota Press. pinyon woodlands of the Great Basin. Creat Basin SMITH, S. J. AND R. S. ANDERSON. 1992. Late Wisconsin Naturnlist Memoirs 2: 119-136. paleoecologic record from Swamp Lake. Yosemite National Park, California. Quaternary Research 3$: Received 17June 1993 91-102. Accepted 4 January 1994