Abstract

Landscape evolution in the eastern Mojave Desert is recorded by systematic changes in Pliocene to latest Pleistocene volcanic land-forms that show discrete periods of eolian deposition, surface stabilization, drainage-network expansion, and erosion on basaltic lava flows. These processes are documented by K-Ar dating in conjunction with morphometric, sedimentologic, pedologic, and geophysical studies. Lava-flow surfaces are composed of constructional bedrock highs and accretionary eolian mantles with overlying stone pavements. The stratigraphy of these mantles records episodic, climatically induced influxes of eolian fines derived from playa floors and distal piedmont regions. The relative proportions of mantle and exposed bedrock vary with flow age, and flows between 0.25 and 0.75 m.y. old support the most extensive eolian mantle and pavement reflecting landscape stability. Drainage networks evolve on flows by (1) rapid initial extension, (2) maximum extension and elaboration, and (3) abstraction of drainage. Increases in bedrock exposures and erosion of the eolian mantle on flows >0.70 m.y. old coincide with maximum drainage extension and significant changes in soil and hydrologic properties within this mantle. Increasing the content of pedogenic clay and CaCO3 causes the accretionary mantle's permeability to decrease; decreased mantle permeability promotes increased runoff, surface erosion, and drainage development. In the late Cenozoic landscape evolution of lava flows, four major stages reflect variations in landscape stability that are controlled by the impact of episodic influxes of eolian fines and increasing soil-profile development on infiltration-runoff properties of the flow surfaces.

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