Abstract The Great Basin is the largest section of the Basin and Range physiographic province (Fenneman, 1930). It includes most of Nevada and western Utah, with fringes extending into Oregon, Idaho, and California (Fig. 1). The basin was named by Fremont (1845), who established that no water drained to the ocean from this huge (>500, 000 km 2 ) region. The Great Basin is an internally drained complex of more than 150 intermontane alluviated basins, separated by about 160 subparallel mountain ranges. Adjoining basins and ranges generally are about the same width, but the basins tend to be longer than their bordering ranges. Mountain ranges typically are elongate, a few being 80 to 190 km long, but some ranges are irregular to almost equidimensional, especially in the Walker fault zone and Mojave Desert. Most of the ranges and basins trend north or northeast but a few are northwest to east-westerly. The northern and central Great Basin resembles a collapsed dome, lowest along its margins, bulging in the center. In western Nevada and western Utah the floors of principal intermontane basins are at altitudes of 1,150 to 1,400 m, and the higher mountain summits are chiefly between 1,800 and 2,500 m, rarely above 3,000 m. In northeastern and east-central Nevada (the highest part of the Great Basin), elevations of intermontane-basin floors are 1,600 to 1,900 m and many mountain summits are above 2,400 m, dominated by Mt. Wheeler (3,984 m). However, in the southern and southwestern one-third of

ABSTRACT The deposits of Pleistocene Lake Tecopa include lacustrine, alluvial, eolian, and groundwater discharge deposits of the Tecopa basin in southeastern California. Stratigraphic sections measured in the Tecopa basin and detailed sedimentary facies analysis were used to interpret the depositional settings and track the evolution of sedimentary processes in the basin during the Pleistocene. The early Pleistocene (ca. 2.4–1.0 Ma) deposits of the Lake Tecopa beds record deposition in small saline, alkaline lakes and playas with surrounding mudflats and sandflats and adjacent alluvial fans. Ancestral Amargosa River gravels are first observed in fluvial deposits in the northern part of the basin at ca. 1.0 Ma and correspond with lake expansions (Glass Mountain [GM] lakes) during deposition of the uppermost Glass Mountain ash beds. Several oscillations in lake level followed the post-GM lake decline, culminating in the basin-filling Lava Creek (LC) lake, which reached its acme during deposition of the 0.63 Ma Lava Creek B ash bed. The post–Lava Creek B strata reflect primarily alluvial, fluvial, eolian, and groundwater discharge depositional processes, punctuated in the youngest part of the section by basin-filling lakes (high lake 1 and 2). The Lava Creek B ash bed and older lacustrine strata exhibit extensive zeolitization and clay authigenesis, characteristic of saline, alkaline lake deposits, but the post–Lava Creek B ash bed lacustrine strata have only minor zeolite and clay alteration, suggesting fresher water conditions and a change in the hydrologic state of the basin. Sedimentological observations along with shoreline elevation data provide evidence for intermittent spillover of basin-filling lakes after ca. 0.63 Ma. Subtle tectonic deformation influenced sedimentary processes in the Tecopa basin throughout its history. Episodes of uplift and tilting of Lake Tecopa strata during the middle Pleistocene in the southern part of the basin along the Tecopa Hump likely controlled the sill elevation for spillover of the lake, creating accommodation space for late Pleistocene basin-filling lakes. Ultimately, decreased uplift could not keep pace with increased discharge resulting from high effective moisture during latest middle Pleistocene pluvial periods, and Lake Tecopa drained, most likely during or immediately after marine oxygen isotope stage (MIS) 10 (ca. 0.3 Ma). The deposits of Lake Tecopa provide a detailed record of Pleistocene paleoclimate from ca. 2.4 to 0.3 Ma that demonstrates Milankovitch-scale tuning and clarifies the amplitude of Pleistocene climate change in the southern Great Basin of North America.