Tertiary and holocene development of the southern sierra nevada and coso range, California

Abstract Eroded remnants of lacustrian sediments, in part pyroclastic units, and containing Middle Pleistocene diatoms, are scattered on an erosion surface on parts of the Coso Range. The surface is, in part, covered by basaltic lavas (K/Ar age 2–3 m.y.) that overlie some sediments (K/Ar age 2.5–3 m.y.) and underlie others. The whole is faulted with some scarps in modern alluvium. The Plio-Pleistocene Coso Formation surrounds the range from Haiwee on the west to Darwin Wash on the north and northeast. Similar deposits are exposed in Panamint Valley, on Argus Range and near Searles Pass. Near Haiwee, the Coso Formation has been displaced vertically more than 3000 and possibly as much as 5000 ft. The White Hills Formation of Blancan age is found well above the floor of Indian Wells Valley. Lacustrian sediments underlie the valley. On the west flank of the Inyo Mts. the Plio—Pleistocene Waucobi beds appear to have been deposited over the present site of the Inyos. From the above, and from field, areal and photographic work, it can be inferred that: 1. (1)An erosion surface, probably the Chagoopa, extended from the vicinity of Mt. Whitney, as far east as the Panamints and east of the Inyos, at the beginning of the Pleistocene. 2. (2)A lake, containing some islands, extended from at least Bishop on the north to Cantil on the south, and from at least the present front of the Sierra to the Panamints during parts of the Pliocene and Early to Middle Pleistocene. It may be the offset equivalent of the Lava Mt. Lake. 3. (3)Uplift of the southern Sierra and the development of Basin and Range topography in this area took place mainly since the eruption of the basalts, and probably since the Middle Pleistocene. 4. (4)Long, linear, N—S-trending, probably right-slip faults pre-existed the uplift and continued south into the Mojave block. 5. (5)These faults were cut off by movement of the Garlock fault. 6. (6)Land north of the Garlock was stretched in an E—W direction from the present Sierra front to beyond Death Valley. To the west of the Sierra it was shoved westward, bending the San Andreas fault. 7. (7)Separation along some of the N—S and E—W faults during the extension led to outpouring of the lava. Basalt filled the voids left by the stretching, transferring heat to the country rock and remelting it in part, giving rise to the andesites and rhyolites found in the area. 8. (8)Normal faulting developed, as extension continued, and differential uplift began. 9. (9)Uplift along the Sierran front first occurred by vertical displacement along the N—S faults and a set of N—W-trending left-slip faults. Segments of the frontal faults are found on the upper block, showing no recent movement there, but upon transition to the foot of the range, they become the active frontal faults with movement continuing to this day. Large landslides developed in the crushed rock at the intersections of the fault systems. 10. (10)The E—W spreading probably began in the Miocene in Washington and Oregon and moved southward, displacing the mass of Sierra westward by the Middle Pleistocene. The activity is still continuing.