Journal of California and Great Basin Anthropology Vol. 12, No. 2, pp. 146-157 (1990), Submerged Tree Stumps as Indicators of Mid-Holocene Aridity in the Lake Tahoe Basin SUSAN LIND STROM, Box 3324, Truckee, CA 95734. A HE surface elevation of Lake Tahoe has in Lake Lahontan for the past 50,000 years the past stood considerably lower than its appears in Benson and Thompson (1987:84). present level for long periods of time. To The Truckee River is "the largest and support this statement, existing paleoenvi- most important stream of the [Lahontan] ronmental evidence and historical documen­ system" (Snyder 1917:34). It joins two great tation of lower lake levels is reviewed. The lakes, Tahoe and Pyramid, the only lakes magnitude of drops in the level of Lake within the Lahontan system that did not go Tahoe is presented in light of new evidence dry in Holocene times (Benson and Thomp­ involving (1) a series of radiocarbon dates on son 1987:80; Miller and Smith 1981). The tree stumps drowned by the rising waters of Truckee River supplies 30% of the discharge Lake Tahoe; and (2) submerged archaeologi­ to the Pyramid Lake and Winnemucca Dry cal features in the lake. The implications of Lake sub-basins (Benson and Thompson 1987: the mid-Holocene lowstands of Lake Tahoe 79). Inflow to Pyramid Lake, other than from are discussed in terms of local and regional the Truckee River, is negligible (Born 1972: paleoclimatic and archaeological trends. 45). During times when Lake Tahoe ceases to spill over into the Truckee River, the PHYSIOGRAPHY river's flow is sustained by its major tributar­ The Lake Tahoe Basin lies at the head of ies (Hardman and Reil 1936:26). the Truckee River drainage, a part of the Crippen and Pavelka (1972:4-5) summa­ larger Lahontan system which covers a total rized the physiography of Lake Tahoe. At an of 40,700 square miles of the western Great average surface elevation of 6,225 feet, and Basin (Fig. 1; Snyder 1917:34). The bathym­ with an area of 191 square miles, Lake Tahoe etry of the Lahontan basin is discussed in is the highest lake of its size in the United Benson and Mifflin (1986). The Lahontan States. It is 22 miles long, 12 miles wide, and basin consists of several sub-basins separated holds 122 million acre feet of water, enough by sills of varying altitude. A sill is the lowest to cover a plane the size of the state of point on the divide separating adjoining sub- California to a depth of 14 inches. The lake basins. Lakes fed by perennial streams (such is the third deepest in North America and the as the Truckee River) that are located in eighth deepest in the world, with a maximum large, wide sub-basins (such as those of Lake depth of 1,645 feet and an average depth of Tahoe and Pyramid Lake) are good recorders 1,000 feet. It is fed by about 100 streams, and of high-amplitude climatic events, as lakes in the Truckee River is its only outlet. these sub-basins rise and fall with changes in The level of Lake Tahoe is naturally climate (Benson and Thompson 1987:70-71). controlled by a narrow sill at Tahoe City, A model chronology presenting fluctuations of where water spills over into the Truckee SUBMERGED TREE STUMPS IN THE LAKE TAHOE BASIN 147 / Winnemucca 1 Lake levation n feet p5,232 Recorded high -6 231 -6 230 Legal limit -6 229 Usual modern sunnmer surface -6 228 elevation range -6 227 Independence Truckee Canal Lake -^. -6 226 Average surface elevation -6 225 Donner Lake -5 224 Natura 1 sill elevat ion -5 223 Lake Tahoe -6 222 1-6 221 Fig. 1. Lake Tahoe and the Truckee River drainage Fig. 2. Historic elevations of Lake Tahoe. basin. River. The elevation of this natural sill is ANCIENT SUBMERGED TREE STUMPS 6,223 feet. However, since the early 1870s, There are trees growing around much of fluctuations of the lake have been artificially the shore of Lake Tahoe on ground just above regulated within a six-foot range by the elevation 6,229 feet. Their large size and construction of a series of small dams at its corresponding age indicate that the lake has outlet. Official measurements, maintained not risen above this elevation during the lives since 1900, show fluctuations ranging from of these trees. Compelling evidence of Lake about two feet below to eight feet above the Tahoe's substantially lower levels comes from natural siU elevation (Fig. 2). The legal limit tree stumps submerged along the south shore, of the lake surface is established at 6,229.10 well below the natural sill (Figs. 3 and 4). feet. The average post-dam surface elevation During the drought of 1934, Harding is 6,225 feet, and the modern summer surface (1965:132-140) observed a cluster of 11 well- elevation, as reported weekly in the local rooted stumps, which had emerged from the newspaper Tahoe World, usually is regulated receding water at Tallac (Fig. 5). These between 6,227 and 6,229 feet. The highest stumps once grew on ground of present known surface elevation, in July 1907, reached elevations up to two feet below the natural siU 6,231.26 feet (Crippen and Pavelka 1972:7). of the lake. Harding (1965) later reported the Since 1900, official measurements record that analysis of three radiocarbon samples taken the lake fell below the level of the natural sill from two of these stumps (Table 1). One eleven times The surface elevation of Lake stump, at an elevation of 6,222.75 feet, dated Tahoe currently is below that of its natural sill at 4,250±200 and 4,790±200 years B.P. The for the second consecutive year. During the remaining stump, at an elevation of 6,222.7 1930s, the level dropped below the natural sill feet, dated at 4,460 ±250 years B.P. for six consecutive years and reached a Six of the stumps observed by Harding recorded low of 6,221.79 feet in December were relocated during a study in 1985 of a 1934 {Tahoe World, AprU 21, 1988, Fig. 2). prehistoric site at Tallac, near the mouth of 148 JOURNAL OF CALIFORNLA AND GREAT BASIN ANTHROPOLOGY Fig. 3. Submerged tree stumps beneath the waters of Lake Tahoe. The stump pictured at the left is 7 feet tall and 3.5 feet across. Taylor Creek (Fig. 5). At this time, the are correct, this may indicate that the tree stumps were deeply submerged below the reached an age of 350 years. Tree-ring counts usual summer surface elevation of nearly on these deeply submerged stumps were 6,228 feet. These submerged features are unobtainable. Stump diameters measured fuUy described and illustrated in Lindstrom between 30 and 45 inches. Harding's rough (1985). Elevations for these six stumps were tree-ring counts on the remaining portions of obtained using an alidade and stadia rod and exposed stumps he observed indicate ages up ranged between 6,223.3 feet and 6,220.7 feet. to 150 years for trees located at the elevation During this study, two more samples were of the sill and 100 years for trees which grew taken for radiocarbon dating from the two feet below the elevation of the siU. The lowermost stump in Harding's cluster estimated age of these drowned trees may (elevation 6,220.70 feet) (Table 1). The indicate a lowstand of Lake Tahoe that sample from the inner core of the stump was stabilized for a period of 100 to 350 years, dated at 4,870 ±60 years B.P. The sample long enough for these trees to become from the outer-most portion of the stump was established and grow to this age. However, dated at 4,520 ±60 years B.P. If these dates such assessments may require adjustment, SUBMERGED TREE STUMPS IN THE LAKE TAHOE BASIN 149 Fig. 4. Submerged tree stumps beneath the waters of Lake Tahoe. The stump shown in the upper photo is the same as shown in Figure 3, left. Both photos by Emory Kristof, (c) National Geographic Society. 150 JOURNAL OF CALIFORNIA AND GREAT BASIN ANTHROPOLOGY pending the ultimate determination of their species. Different pines vary in their ability to tolerate high water tables. During 1989-1990, 15 more stumps were discovered between Emerald Bay and State- Une at or below the level of Lake Tahoe's natural sill: nine are along Baldwin Beach, one is at the mouth of Emerald Bay, four are at Al Tahoe, and one is at El Dorado Beach in Stateline (Fig. 5). Samples were extracted from most of these stumps. They were taken from different places on the stumps and exact sample locations were not consistently record­ ed. Consequently, dates may vary depending Glenbfook on exactly where in the array of growth rings the sample was obtained. Stump depths were measured from a tape measure, which ex­ tended from the base of the stump to the Zephyr Pornt D L BNss Stale Paik surface of the lake. Depths were then com­ Elk Point Emerald Bay puted from the official surface elevation, pub­ Slaletine lished weekly in the newspaper Tahoe World. Baldwin Beach South Lake Tahoe Most of these stumps are weU preserved. TaYlor Cr The deepest stump is over seven feet tall and 3.5 feet across. The stumps located farthest below Lake Tahoe's rim probably have not Fallen Leal Lake been exposed long to air since they were first submerged; otherwise, they would since have decayed.