Late Quaternary geomorphology and soils in Crater Fault, Yucca Mountain area, southern Nevada

Soil-geomorphic studies indicate that six major allostratigraphic units occur in Crater Flat, Nevada, adjacent to Yucca Mountain. These units are, from youngest to oldest, Crater Flat, Little Cones, Late Black Cone, Early Black Cone, Yucca, and Solitario. Stratigraphic order and soils allow correlation with similar alluvial sequences in adjacent Basin and Range areas. Rock-varnish ¹⁴ C AMS ages on Late Black Cone and younger units, and K-Ar ages from volcanic lava cones, provide calibration points for a Crater Flat cation-leaching curve. This curve differs somewhat from a previous Yucca Mountain curve and yields calculated cation-ratio ages younger by factors of two to three for the younger units. The Little Cones and Late Black Cone units collectively form an extensive late Wisconsin-early Holocene deposit not previously described in Crater Flat. The Late Balck Cone unit (>17 to >30 ka) correlates with units in the Lower Colorado River, Death Valley, Mojave Desert, and Las Vegas areas- all likely products of climatically induced, late Wisconsin pluvial alluviation. Similarly, the Little Cones unit (>6 to >11 ka) correlates with regional units thought related to alluviation during climatic transition from the late Wisconsin maximum pluvial to the arid Holocene. -from Authors