The Upper Las Vegas Wash Conservation Transfer Area (ULVWCTA) provides habitat for two of Nevada's special status plant species, Arctomecon californica Torrey and Frémont (ARCCAL) and Eriogonum corymbosum Bentham var. nilesii Reveal (ERICOR).  To aid the Bureau of Land Management Las Vegas Field Office in conservation-based decision-making, we created a refined soil map focusing on soil-geomorphic relationships and characterized the soils associated with these plants of interest (POIs).  We used a Geographic Information System (GIS), original SSURGO polygon lines, high-resolution aerial photography and digital terrain models, and Landsat and ASTER spectral data to refine the soil map. Forty-five soil pedons representing typical soil-landform-vegetation units were described, sampled, and analyzed to  help develop and document the refined map.  We sampled and characterized 658 surface soils (0-8 cm) as part of a vegetation sampling of the ULVWCTA and a POI survey on the basin floor.   

Results/Conclusions

POIs occur in map units on spring deposits and basin floor sediments that lack a thick gravel veneer: Las Vegas gravely fine sandy loam, 0 -2% slopes; and Badland.  These CaCO₃-rich soils have petrocalcic horizons or carbonate nodules within 100 cm, and exhibited relict redoximorphic features, indicating they may be exhumed late-Pleistocene paleosols.  Pedons in these units had <0.1-5.0% gypsum in the subsoil, but lacked gypsum in surface horizons.  The first-to-third quartile ranges of surface pH, estimated clay%, bulk density, and calcified fragments ≥2-mm for POI points were 8.4-8.6, 12-16%, 0.84-1.06 Mg m^-3, 96-100%, respectively, and for shrub points were 8.2-8.4, 10-14%, 0.91-1.23 Mg m^-3, 0-70%, respectively.  These data indicate the relatively narrow distribution of POIs on the basin floor compared to the wide distribution of shrubs on alluvial fans, the basin floor, and in drainage-ways.  In the POI survey, surface soil properties differed little between the ARCCAL presence, ERICOR presence, and POI absence points on the basin floor. While it has been suggested that the POIs  are gypsophiles, gypsum was rare in all surface soils.  Geomorphic surface (e.g., spring deposit, basin floor) and soil map unit  are better indicators of POI potential habitat than surface soil chemistry.