Abstract
The purposes of this study were a) to statistically classify rocky, upland desert soils on a fault-block ridge at Yucca Mountain, Nevada, by geomorphology and physical properties affecting infiltration, and b) to evaluate the genesis-lithology-qualifier (GLQ) mapping method as a basis for this classification. Map-unit soils were sampled for grain-size distribution (texture), total-soil bulk density, fine-soil bulk density, rock-fragment bulk density and porosity, and slope, aspect, and position. Relations between geomorphic environments and physical property variables were evaluated using correlation and analysis-of-variance techniques, and statistically distinct map units were determined for GLQ mapping using multiple comparison technique. Hydraulic-conductivity values for each map unit were estimated based on mean silt and clay content.
Statistical analyses indicated that fine-soil bulk density was related to slope position and that soil texture was more related to soil genesis than any other geomorphic variable. The bead-cone, irregular-hole, bulk-density-sampler method was used to provide the most accurate data for the steeply sloping conditions in the study area.
The mapped soils were classified statistically as a residuum unit, a colluvial (creep) unit, a colluvial (creep-talus) unit, and a slide (flow) unit. Most often, textural variables of surficial soils were statistically distinct among the final map-unit soils. Estimates of saturated hydraulic conductivity of the four GLQ units ranged from 5.4 × 10−5 cm/sec to 5.9 × 10−6 cm/sec; these values may not be statistically different.
Characteristic soil-horizon sequences were identified for each GLQ map unit, including a well-cemented caliche horizon in the slide (flow) unit, well-developed illuviation in the residuum unit, and statistically large mean surficial cobble counts in the colluvial (creep-talus) unit. These sequences, combined with the statistical distinction of textural variables among the GLQ map-unit soils, indicate that the GLQ map may be used as a valid system of hydrologic classification of soils and to estimate potential water infiltration.