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Southern California Areal Mapping Project

Geologic Framework of the Northwestern Coachella Valley

| Selected References |

Geologic-mapping Investigations

SCAMP currently is conducting geologic-mapping investigations to clarify the geologic setting and geologic history of the northern Coachella Valley. The goal is to describe the physical properties of rock and sediment, to determine the distribution and movement history of fault systems, and to provide a geologic-map basis for evaluating earthquake potential, industrial-mineral resources, and ground-water resources.

The northwestern Coachella Valley is the alluviated lowland that extends southeastward from the San Gorgonio Pass region to the north end of the Salton Sea. The lowland is traversed by multiple strands of the San Andreas fault, and is punctuated by localized compressional squeeze-ups that form dome-shaped hills of uplifted sand and gravel. Current geologic understanding suggests that the lowland is a contractional region that has developed over the last 1 million years or so in response to left steps among various strands of the San Andreas fault. This left step still is taking place today, and provides the background for current earthquake activity in the northern Coachella Valley region. Sedimentary materials that are filling up the basin record information about interactions among the various fault systems, including their origin and movement history. The sediments also store ground water for the Coachella Valley region, and have been utilized for sand-and-gravel resources.

SCAMP's objective in the northern Coachella Valley is to determine its geologic framework and geologic history. Although the region does not have the population density of the more urbanized Inland Empire to the west, geologic studies in the Coachella Valley are relevant for several reasons:

 

  • the Quaternary displacement history of the San Andreas fault strands is not well documented;
  • ground-water withdrawal and recharge are occurring in an arid setting where the shape, thickness, and physical stratigraphy of subsurface basins are not completely understood;
  • extensive luxury-resort growth has triggered extensive infrastructure development and service communities that are growing at a rapid rate;
  • extensive tracts of Quaternary and Tertiary sand-and-gravel deposits are incompletely understood in terms of their stratigraphy, physical properties, and age, and their potential for development as industrial resources has not been systematically evaluated;
  • Mission Creek and Whitewater River, two major drainages in the Coachella Valley, are significant sources for streamflows that historically have recharged the Salton Sea and its geologic predecessors (lake Coahuila). The Quaternary evolution of the Coachella Valley sedimentary fill thus is relevant to environmental and ecosystem studies of the Salton Sea.

For FY 2001, SCAMP geologic-mapping, pedogenic, and stratigraphic investigations will focus on the northwest end of the Coachella Valley, where multiple strands of the San Andreas fault zone appear to have stepped left into the San Gorgonio Pass structural knot in the San Andreas, thereby bypassing the southeastern San Bernardino Mountains and creating several dome-like squeeze-ups that have brought older Quaternary sedimentary materials to the surface. The domal uplifts are being dissected while late Quaternary surficial deposits simultaneously are being deposited around them on the Coachella Valley lowland.

Recent SCAMP Products

Matti, J.C., Morton, D.M. and Cox, B.F., 1992, The San Andreas fault system in the vicinity of the central Transverse Ranges province, southern California: U.S. Geological Survey Open-File Report 92-354, 40 p., scale 1:250,000.

Matti, J.C., and Morton, D.M., 1993, Paleogeographic evolution of the San Andreas fault in southern California: a reconstruction based on a new cross-fault correlation, in Powell, R.E., Weldon, R.J., II, and Matti, J.C., eds., The San Andreas fault system: displacement, palinspastic reconstruction, and geologic evolution: Geological Society of America Memoir 178, p. 107-159.


Geophysical Investigations

SCAMP is co-sponsoring geophysical studies of the northern Coachella Valley that will lead to a 3-D geologic/structural/physical-property model. This model will provide a basis for estimates of seismic velocity in various geologic media, which in turn will be used for earthquake ground-shaking estimates, for ground-water flow modeling, and for estimates of potential for ground-water recharge.

Recent SCAMP Products

Ponce, D.A., and Langenheim, V.E., 1992, Isostatic residual gravity map of the Palm Springs 1:100,000 quadrangle, California: U.S. Geological Survey Open-File Report 92-702, scale 1:100,000.

Jachens, R.C., 1992, Aeromagnetic map of the Palm Springs 1:100,000 scale quadrangle, California: U.S. Geological Survey Open-File Report 92-549, scale 1:100,000.


Cooperative Interactions

SCAMP geologic investigations in the northern Coachella Valley are coordinated with several USGS projects. These cooperative investigations include:

 

Geologic framework for earthquake studies:

The USGS Earthquake Hazards Program sponsors earthquake investigations in southern California, including investigations of ground-shaking potential, earthquake monitoring, and earthquake history. The California Geologica Survey has a program of earthquake-fault mapping and zonation designed to recognize fault lines and to outline setback guidelines. Geologic-mapping studies by SCAMP are coordinated with these earthquake investigations, and are designed to clarify the distribution, origin, and history of faulting within the Coachella Valley region.

Geologic framework for mineral-resource studies:

The USGS Mineral Resources Program sponsors assessments of sand-and-gravel resources through its National industrial minerals project (NIM). SCAMP and the NIM Project hope to develop procedures for collecting, digitally attributing, and analyzing geologic information relevant to resource assessments of surficial geologic materials in arid and semi-arid climatic settings. We hope to identify parameters (physical properties, age, geomorphic setting, post-depositional history, pedogenic soils) that can be routinely collected by general-purpose geologists, attributed for storage in digital geologic-map files, and retrieved for analysis within a GIS that uses digital geologic-map data bases as a core information layer. These efforts will be coordinated with mineral-resource investigations conducted by the California Geological Survey.

Geologic framework for ground-water studies:

Ground-water withdrawal and replenishment in the northern Coachella Valley are monitored by several agencies, including the Colorado River Regional Water Quality Control Board and the Desert Water Agency and the Department of Water Resources, Southern District. SCAMP will provide geologic-map data to these entities as the data are developed.

 

Useful websites related to the Coachella Valley and Salton Trough:

http://www.sci.sdsu.edu/salton/geology_of_the_salton_basi.htm http://www.sci.sdsu.edu/salton/SaltonBasinHomePage.html http://www.sci.sdsu.edu/salton/SaltonSeaHomePage.html

| Selected References | Return to "Where is SCAMP Currently Working?" |

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This site last updated September 3, 2004 (ps)

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