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San Andreas Fault System in Southern California (SAFSOC)

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TASK 2 - Joshua Tree National Park Studies

Task Leader: Robert Powell

Statement of Problem:
The eastern Transverse Ranges province is characterized by a set of sinistral east-trending faults that interact with the San Andreas Fault along the western margin of the province and with the northwest-trending dextral faults of the Mojave Desert province to the north and east. This sinistral domain forms a direct link between the San Andreas Fault Zone and the Eastern California Shear Zone and logically its strain budget should be considered as part of the latter. Faults of the eastern Transverse Ranges sinistral domain and the Mojave Desert dextral domain form a conjugate fault system in which wedge-shaped basins of variable depths form in the acute intersections between faults of the two sets. The interaction between faults of the eastern Transverse Ranges sinistral domain and the San Andreas Fault Zone is less straightforward and the currently active transition between the two contains arrays of seismic north-trending faults. Sequences of erosion surfaces in the crystalline-rock highlands-the timing and mechanisms of their development, their three-dimensional distribution, and the pathways by which eroded materials were transported into adjacent lowlands-are key to understanding landscape evolution in the crystalline terrane of southern California. These bedrock surfaces and sequential relations among them are particularly well developed and well preserved in the eastern Transverse Ranges and adjoining parts of the western Mojave Desert. Magnitude and timing of deformation and fault displacements of these widespread basement-rock surfaces offer the potential for quantifying off-fault strain accumulation and fault-related effects during a time-frame much younger than that constrained by the basement units themselves. empty box graphic
Joshua Tree with granite outcrop in Joshua Tree National Park, CA
Joshua Tree with granite outcrop in Joshua Tree National Park, CA
Granitic domes (plutons) in Joshua Tree National Park, CA
Granitic domes (plutons) in Joshua Tree National Park, CA
Objectives: (1) Investigate the character, age sequence, correlation, and geologic and geomorphic history of erosional landforms in basement highlands. Continue to investigate the regional geologic framework of the crystalline rocks, in part because the BALANCE landscape-evolution approach requires that we understand relations between surface-development and underlying basement units and structures. As resources permit, construct a GIS database layer and three-dimensional model showing the distribution and sequence of basement surfaces in the eastern Transverse Ranges and western Mojave Desert. Develop a landscape-evolution model integrating weathering, stripping, and sedimentary overlap events associated with the surfaces. (2) Because one does not currently exist, produce a geological and geophysical map of Joshua Tree National Park at a scale of about 1:50,000.  

Methodology:
(1) Identify and map erosional basement surfaces in relation to bedrock units (crystalline and sedimentary) on which they are formed, with emphasis on their relative chronology and mutual spatial relations and on distinguishing characteristics.
(2) Map and characterize sedimentary, volcanic, and pedogenetic sequences that overlap the surfaces.
(3) Map and characterize sedimentary sequences deposited in adjacent basins as the surfaces were formed.
(4) Identify provenance and transport pathways for sediment in basin sequences.
(5) Use spatial patterns for each surface and for the surface sequence as a whole to elucidate regional strain history as recorded by uplifted, warped, and (or) folded surfaces and by any surface disruption by faulting

Task Products:
Map, Planned: Powell, R.E., Matti, J.C., Cossette, P.M., and Langenheim, V.L., 2011, Geologic and Geophysical Map of
Joshua Tree National Park, USGS, Scientific Investigations Map
 

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