What We Know and Need to Know About Hydropedology in California.

Ten years of investigating hydrological and pedologic relationships in the Sierra Foothill Region has yielded more questions than answers. Soil landscape relationships vary in complexity across the region. Soils derived from granitic bedrock show systematic variability in soil properties. Thus, our ability to describe hydrological processes is relatively high. In metavolcanic terrain, soil variability appears to be random. Terrain variables alone accounted for approximately 30% of the variance in soil properties at the granitic catena, but only 4% at the metavolcanic site. While we have accurately described hydrologic flowpaths, our ability to predict soil moisture dynamics in space and time is low, especially in soils derived from metavolcanic parent material. Our findings suggest that the predictive capacity and interpretation of DEM-derived terrain shape indices can vary widely in time, depth, and space. Accurate prediction of soil moisture dynamics and soil properties with terrain indices in catchments containing well-developed soils may require additional diagnostic attributes. Soil survey in the Foothill Region of CA only generally describes soil variability because the cartographic scale is fairly broad.  Land use in this region has placed unforeseen demands on soil survey reports. More information about soil variability at higher spatial resolution is needed.