Geomorphology and soil physical and chemical characteristics strongly influence plant community composition.  The degree to which these abiotic factors control community composition compared to biotic factors is not well understood.  We investigated the relationship of plant communities to a variety of geomorphological and soil characteristics on a 20,000 acre tract in the Upper Las Vegas Wash, Nevada that contained a complex mosaic of abiotic factors and plant communities in order to assess what were the most important, community-controlling factors.  Of special interest were two threatened plant species, Arctomecon californica Torrey and Frémont and Eriogonum corymbosum Bentham var. nilesii Reveal which, based on preliminary results, are highly associated with a specific geologic substrate and soils with unique physical and chemical properties compared to those of the surrounding area.  Results of these studies may inform potential actions taken to conserve, restore or manage desert plant communities.