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The Great Basin Pliocene-Pleistocene Lake Tecopa in southeastern California formed in part due to dammming of the ancestral Amargosa River by an antiformal uplift known as the Tecopa Hump. Previous studies concluded that tectonic processes were inconsequntial to lake deposition. Here four stratigraphic sections are measured, described, and compared to sections previously done throughout the basin to discern tectonic influences on lake processes. The southern Tecopa Basin is characterized by a tectonically controlled fan-delta complex intertonguing lacustrine sediments. Joint orientations and bedding attitudes collected on three time horizons, the Lava Creek B tuff (665 ka), Bishop tuff (758 ka), and the C Tuff (2.1 Ma), suggest at least 50 m of uplift during the Quaternary associated with highly variable stress field perturbations. Rising lake level most likely competed with uplift such without uplift lake spillover into southern Death Valley would have occured earlier. .
Stratigraphic units in the Tecopa basin, located in southeastern California, provide a framework for interpreting Quaternary climatic change and tectonism along the present Amargosa River. During the late Pliocene and early Pleistocene, a climate that was appreciably wetter than today's sustained a moderately deep lake in the Tecopa basin. Deposits associated with Lake Tecopa consists of lacustrine mudstone, conglomerate, volcanic ash, and shoreline accumulations of tufa. Age control within the lake deposits is provided by air-fall tephra that are correlated with two ash falls from the Yellowstone caldera and one from the Long Valley caldera. Lake Tecopa occupied a closed basin during the latter part, if not all, of its 2.5-million-year history. Sometime after 0.5 m.y. ago, the lake developed an outlet across Tertiary fanglomerates of the China Ranch Beds leading to the development of a deep canyon at the south end of the basin and establishing a hydrologic link between the northern Amargosa basins and Death Valley. After a period of rapid erosion, the remaining lake beds were covered by alluvial fans that coalesced to form a pediment in the central part of the basin. Holocene deposits consist of unconsolidated sand and gravel in the Amargosa River bed and its deeply incised tributaries, a small playa near Tecopa, alluvial fans without pavements, and small sand dunes. The pavement-capped fan remnants and the Holocene deposits are not faulted or tilted significantly, although basins to the west, such as Death Valley, were tectonically active during the Quaternary. Subsidence of the western basins strongly influenced late Quaternary rates of deposition and erosion in the Tecopa basin.
A study of the structural contrast between the little-deformed rocks of the Sebastopol block and the highly deformed rocks of the Santa Rosa block.