U.S. Geological Survey

The response of desert plant assemblages to disturbance was studied in Death Valley National Monument, California. Plant assemblages on debris flows, alluvial terraces, five abandoned townsites, and a pipeline corridor were measured to quantify recovery rates and to develop a model of change in desert vegetation.

We studied shrub communities in the Panamint Mountains of the Mojave Desert to determine whether vegetational changes after disturbance can be characterized as "succession" according to modern successional theory. We found, on a variety of disturbed and undisturbed sites, that the rate of change was a function of the type and age of disturbance.

The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from human activities.

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Stratigraphic, lithographic, and structural features of younger Precambrian rocks of southern Arizona as a basis for understanding their paleography and establishing their correlation.