Journal of California and Great Basin Anthropology Vol. 1, No. 2, pp, 280-294 (1979), The Altithermal Revisited: Pollen Evidence from the Leonard Rockshelter ROGER BYRNE COLIN BUSBY R. F. HEIZER URING the past thirty years, there has sistence and settlement patterns? In this paper, Dbeen a continuing debate among we present evidence that relates directly to the students of Great Basin prehistory over the first question and indirectly to the second. nature and significance of postglacial climatic More specifically, we report on the fossil change (Aikens 1970; Antevs 1948; Aschmann pollen content of two series of sediment 1958; Baumhoff and Heizer 1965; Bryan and samples from the Leonard Rockshelter, Gruhn 1964; Harper and Alder 1970; Jennings Pershing County, Nevada. 1957; Martin 1963; Swanson 1966). Several Leonard Rockshelter (NV-Pe-14) is one of symposia have been devoted to the subject a limited number of sites in the Great Basin (Fowler 1972, 1977; Elston 1976), but there with a clear record of human occupance that are still no signs of a consensus. One basic dates back to the early Hoiocene. The site was issue is the validity of the Antevs three- excavated in 1937 and 1950 by University of part model. Mehringer (1977), for example, California archaeological field parties and has cautioned against the acceptance of paleo- produced a varied assemblage of artifacts. climatic models which claim relevance for the Wooden atlatl foreshafts have been radio­ Great Basin as a whole. The question remains, carbon dated at 7038 + 350 B.P. (5088 B.C.), however, as to whether or not the Antevs' and indirect evidence in the form of obsidian reconstruction is valid. Was the Altithermal, flakes from a basal bat guano layer radio­ for example, a period of warmer and drier carbon dated at 11,199 ± 570 B.P. indicates climate? And, if so, was it warm and dry that the site may have been occupied as early as enough to account for changes in human sub- 9000 B.C. (Heizer 1951). Roger Byrne, Dept. of Geography and Museum of Paleon­ The site is also of interest in that it provides tology, Univ. of California, Berkeley, CA 94720. Colin Busby, clear evidence of environmental change during Dept, of Anthropology, Univ, of California, Berkeley, CA the Hoiocene. The rockshelter was formed by 94720. R, F. Heizer, Dept. of Anthropology, Univ, of Cali­ wave action along the southern shore of an arm fornia, Berkeley, CA 94720 (deceased). of Pleistocene Lake Lahontan, and has since [280] THE ALTITHERMAL REVISITED 281 been partially filled by a distinctive sequence of Humboldt Sink (Fig. 3). The Humboldt River sediments, including beach gravels, bat guano, drains through this area into Humboldt Lake. aeolian silt, and rockfall. In 1950, Antevs inves­ The lake is now shallow (<20 ft. deep) and tigated the stratigraphy of the site and during the historic period has been highly interpreted it as supporting evidence for his variable in area. In 1883, for example, it reconstruction of postglacial climatic change covered an area of 20 mi.^ and the eastern in the Great Basin (Antevs 1955). In 1955, in shoreline was less than a mile from the rock­ the hope of obtaining further evidence on the shelter. In 1951, however, the lake had an environmental history of the site, Heizer sent area of only 11 mi.-, and the eastern shoreline H. P. Hansen (Oregon State University) was more than seven miles from Leonard (Fig. samples of guano for pollen analysis. Unfor­ 2). During the period of European settlement, tunately, the results proved to be negative and irrigation has drastically reduced the flow of no further pollen work was attempted at that the Humboldt River and during drought years time. the lake has dried up completely (Antevs In this paper, we report on a second 1938). This recent variability in the area of attempt to recover pollen from the Leonard Humboldt Lake underlines the fact that even Rockshelter sediments. In 1976, we directed small changes in hydrological conditions can our attention to two series of samples that have significant effects on a shallow lake of included the whole of the stratigraphic this kind. We shall reemphasize this impor­ sequence. The samples were collected during tant point later in the paper. the 1950 excavation, and had since been stored The present climate of this part of Nevada in the Lowie Museum of Anthropology is semi-arid. Mean annual precipitation totals (Berkeley). Like Hansen, we found it impos­ vary from the less than 5 in. at 3800 ft. to sible to extract pollen from the lower bat 30-35 in. at 8000-9000 ft. Most of the precipi­ guano layer, but the overlying silt and rock- tation is received in winter from mid-latitude fall layers yielded reasonably well-preserved cyclones, although summer thunderstorms pollen in countable quantities. The results of can also produce locally significant totals. the analysis in large part support the Antevs The annual temperature regime is character- model and also throw new light on the "sig­ nificance" of climatic change in the Great / Basin. l. c^^' ^'1- _ ^ ^ \ THE REGIONAL SETTING ; •• / X ' (-study Location Leonard Rockshelter is located 17 miles ^"'"'^ M \ ''' -x 1 south of Lovelock, Nevada, on a north-facing ' ''} } slope of the West Humboldt Range (Figs. 1 1 Jfiml r^' and 2). This area of the Great Basin has numerous cave and open sites, several of which V i ( \ \ ^ ' have been excavated or surface collected VJ • I'M (Loud and Harrington 1929; Heizer and ( 1 1 1 \ \ f^ ' ~ T Krieger 1956; Roust 1966; Baumhoff 1958; ) , Elsasser 1958; Heizer and Clewlow 1968; [. 1 1 ' 1 Heizer and Napton 1970; cf. Ranere 1970 for an overview). Less than a half-mile to the west Fig, 1. Location of the study area within the Great of the site is the broad and flat expanse of the Basin, 282 JOURNAL OF CALIFORNIA AND GREAT BASIN ANTHROPOLOGY istically continental with hot summers and semi-arid nature of the climate and is domi­ cold winters; Lovelock, Nevada, for example, nated by several species of xerophytic shrubs. has a mean January temperature of 27°F. and On a regional scale, the site is close to the a July average of 75°F. (Brown I960). boundary between the Sagebrush-Grass Zone The vegetation of the area reflects the of the northern Great Basin and the more 8 - LEONARD ROCKSHELTER -^ '-"' ,.-...AOOO -HUMBOLlir ^:'^OVELOCK'CAVE ;>r I.".-'- *;•,.• ••••'.'J..* "v-;.'"•-'•;. V ^•;f'- " ;'.'.-!.''.• 'SINK\:.:>ft' A • . • i:.-.. -"/- 4684 •••'.-,••'"'.•'•,' ^- ^ ' ~ - ' -•,'^'i'^'i**'f-'r-'-'-.''.V.^ A. •/•..• ."'.I ^ .'-; -';•: ..'*-^.,'- --'"•'•":,•':•• >V-- OCAJ_A* -CAVE r J 1882 lake level (3929') + Surface site -W^:: Alkali flat O 5 Miles •'I---':;-' •4 Contour interval 500' O 8 Km Fig, 2, Map of the study area indicating major topographic and cultural features. THE ALTITHERMAL REVISITED 283 Fig. 3. The Humboldt Sink from the Leonard Rockshelter. centrally-located Shadscale Zone (Billings marsh covered the area to the north of the sink. 1951:104). Local variation in species com­ Most of this area has since been reclaimed for position is largely a function of edaphic con­ agriculture by deep drainage canals, and only ditions. The following summary is based on a few relic areas remain. The dominant species Billings (1951) and Cronquist et al. (1972). here are cattail {Typha dotningensis) and tules On the higher ground, sagebrush {Arte- {Scirpus americanus, S. acutus). mesia tridentata) is the dominant species. THE SITE AND ITS STRATIGRAPHY On the lower slopes and on the well-drained Lahontan sediments, greasewood {Sarcobatus In 1936, the Leonard Rockshelter was baileyi) and shadscale {Atriplex confertifolia) mined for bat guano by Thomas Derby. are more important. These spiny shrubs are During the mining operation, Derby dis­ generally evenly spaced and provide a rather covered and saved several artifacts which thin cover. Other species less commonly en­ were later described by Heizer (1938). In 1937, countered are bud sagebrush {Artemisia a University of California field party made spinescens). Mormon tea {Ephedra nevaden- some preliminary archaeological investi­ sis) hop sage {Grayia spinosa), and winter fat gations at the site, and several more artifacts {Eurotia lanata). Perennial herbs and annuals were recovered from a basal guano layer. It may have been more common prior to grazing was recognized at the time that these artifacts by cattle and sheep, but are now rare. On might represent an early period of occupation, clayey soil and in poorly drained depressions although no means of absolute dating were at the edge of the sink greasewood {Sarcobatus then available. In 1949, samples of the guano vermiculatus) is dominant, but gives way to and three greasewood atlatl foreshafts were iodine bush {Allenrolfea occidentalis), salt- sent to W. F. Libby for radiocarbon dating. grass {Distichlis spicata var. strict a), and The dates proved to be unexpectedly old, Salicornia europaea subs, rubra on the more 8600 ±300 B.P. (6710 B.C.) and 7038 ±350 xeric sites. Cottonwoods {Populus fremontii) (5088 B.C.), respectively (Arnold and Libby form gallery forests along the river, and sage­ 1950), and it was therefore decided to exca­ brush {Artemisia tridentata) is also encoun­ vate the site more thoroughly. A University tered in the valley bottoms. During the nine­ of California field party spent five weeks at teenth century, extensive areas of freshwater the site in 1950 and established the natural 284 JOURNAL OF CALIFORNIA AND GREAT BASIN ANTHROPOLOGY stratigraphy and history of human occupance. guano layer in Areas B and C. The guano The results of this excavation were presented accumulated over a period of 4000 years as in a preliminary report by Heizer (1951). indicated by a date of 7038 B.P. for the atlatl During the 1950 excavation, four areas of the foreshafts near the top of the deposit.