SOILS AND GEOARCHAEOLOGY OF LA JARA CREEK, HOT CREEK, AND THE ALAMOSA RIVER, UPPER RIO GRANDE BASIN, COLORADO

This study examines soil development on alluvial landforms in La Jara Creek, Hot Creek, and the Alamosa River, upper Rio Grande basin, San Luis Valley, Colorado. Objectives of the study are to (1) identify and describe sediments, soils, and landforms, (2) model the temporal and spatial patterns of landscape evolution using soil-stratigraphic relationships, and (3) work toward the development of a predictive model for locating cultural deposits in the stream valleys, based on where sediments of a particular age are stored. Results indicate a gradational, temporal pattern of sediment storage beneath the low-terraces (T-1) in the Alamosa River valley. Based on soil development, the T-1 fill along the Alamosa River appears to be older and more stable in the lower reaches of the stream, relative to the upper reaches. Further soils data suggest that the high-terraces (T-2 fills) at the La Jara Creek and Hot Creek localities, exhibiting Btk and Bk horizons respectively, have been stable for a longer period than the T-2 fill at the Alamosa River locality, characterized by stacked A-C profiles. Buried soils are present beneath the T-2 surface in all three river valleys. Cultural deposits were recorded in the buried A horizon of the T-2 fill at Hot Creek and as surface finds on the T-2 terrace at La Jara Creek. An organic mat at the base of the Alamosa River T-1 fill and bulk carbon from the buried soils will provide radiocarbon evidence for the ages of the fills.