SOILS AND GEOARCHAEOLOGY OF THE UPPER RIO GRANDE BASIN, SAN JUAN MOUNTAINS, COLORADO

This study examines soil development on alluvial landforms in the Upper Rio Grande Basin. 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. The study focused on two areas: the South Fork study area and the Rio Grande study area. Both locations have a system of four terraces. Research methods include field mapping of fluvial terraces, field and laboratory analysis of soils, GIS, and archaeological surveys. Cultural deposits, including flakes and projectile points, were recorded as surface finds on both the T4 and T3 terraces. Preliminary radiocarbon data suggest that the lower terrace (T4) is less than 3,200 ¹⁴C years old. The T4 terrace fill is characterized by weakly developed buried soils and cumulic development. Based on radiocarbon data, the highest terrace (T1) is Pleistocene outwash from the last glacial maximum. As a result, archaeological deposits in these terrace fills could relate to Clovis and pre Clovis cultures. In the summer of 2016, fifteen additional 14C and OSL samples were collected and will help to identify relationships between terraces and the potential for archaeological materials.