The Quaternary alluvial sequence of the Antelope Valley, California

Abstract

Arkosic alluvium derived from the Transverse Ranges and Tehachapi Mountains and deposited in the closed basin of the Antelope Valley, California, can be subdivided into eight mappable units. The six oldest units range in age from less than 0.5 m.y. through early Holocene and form widespread fill terraces and fans that extend over several thousand km 2 of the valley floor. In contrast, the two youngest units, which consist of late Holocene and modern floodplain and channel sediments, are thin and of limited areal extent. The youngest of the six older deposits can be physically traced into nearly all drainages along both mountain ranges, which suggests nearly synchronous deposition across the region during latest Pleistocene to early Holocene time. These deposits appear to interfinger with and overlie pluvial lake deposits. The five older deposits can be recognized and correlated based on a combination of several factors such as similarity of soils, in situ shear-wave velocities, and degree of primary surface dissection. This evidence suggests that principal alluviation was regionally synchronous during the middle and late Pleistocene as well.The existence of a pervasive and uniform sequence of apparently synchronous deposits throughout the region suggests that major aggradational and degradational episodes are controlled by regional climatic fluctuations. The existence of buried soils that require long periods of time for their formation further supports a climatic control of alluviation by suggesting that principal alluvial deposition is rapid and episodic. Finally, sedimentological evidence that indicates a change in hydrologic conditions during principal alluviation and an apparent correlation among major units in the Antelope Valley to those in the eastern San Joaquin Valley strongly suggest that aggradational episodes occur during major glacial to interglacial climatic transitions.

Geologic map database of the El Mirage Lake area, San Bernardino and Los Angeles Counties, California

“…The soil development north of the lake closely matches changes in micro-topography of alluvial surfaces, both of which correspond to soils and micro-topography nearby (McFadden and Weldon, 1987), in the central Mojave Desert (Yount and others, 1994), and in the San Joaquin Valley (Ponti and Burke, 1980). This correlation indicates that much of the piedmont north of El Mirage Lake is composed of deposits tens of thousands to hundreds of thousands of years old.…”

“…Much of the map area was mapped in reconnaissance by Ponti and Burke (1980), who distinguished pediments, alluvium of Holocene and Pleistocene age, and eolian and playa deposits. Our more detailed mapping has subdivided these units and distinguished several ages of alluvial cover on the pediments.…”

“…Quaternary faults were shown by Dibblee (1960) and Troxel and Gunderson (1970) along the southwest flank of the Shadow Mountains; the principal fault was named the Mirage fault by Dibblee (1960). The Mirage fault is a system composed of three segments about 6 to 10 km long that together are about 23 kilometers long (Ponti and Burke, 1980). Ward and others (1993) mapped more faults as the extension of the Mirage fault farther to the northwest where it crosses the Rogers Lake playa and continues northwest along the Bissell Hills.…”

“…2). The map includes detailed geology of surface and bedrock deposits, which represent a significant update from previous bedrock geologic maps by Dibblee (1960) and Troxel and Gunderson (1970), and the surficial geologic map of Ponti and Burke (1980); it incorporates a fringe of the detailed bedrock mapping in the Shadow Mountains by Martin (1992). The map data were assembled as a digital database using ARC/INFO to enable wider applications than traditional paper-product geologic maps and to provide for efficient meshing with other digital data bases prepared by the U.S. Geological Survey's Southern California Areal Mapping Project (http://geology.wr.usgs.gov/wgmt/scamp).…”

The application of satellite differential SAR interferometry-derived ground displacements in hydrogeology

“…Consolidation tests on select cores indicated the lacustrine deposits were consolidated (Peter Martin, US Geological Survey, unpublished data, 2006). In contrast, the lacustrine units northeast of Lancaster near Rogers Lake are probably less than 14,000 years old (Ponti 1985), underconsolidated and more compressible than those at the Lancaster extensometer site . Subsequent models have simulated subsidence using smaller compressibilities and larger preconsolidation stresses in the region south of Lancaster based on the InSAR observations and the core analyses (Hoffmann et al 2003a;Leighton and Phillips 2003), and have achieved good agreement with the observations.…”