THE RELATIONSHIP BETWEEN SOIL DEVELOPMENT ON MORAINES AND TERRACES IN THE RIO GRANDE HEADWATERS OF SOUTH CENTRAL COLORADO

Continuing research in the summer of 2014 was conducted to determine the relationship of soil development on newly mapped glacial moraines with nearby stream terraces at two locations in the upper reaches of the Rio Grande watershed. At these two sites, moraines are in close proximity to multiple river terraces. The first site (ele. ~2550 m), located just west of the town of South Fork, CO on the South Fork of the Rio Grande exhibits multiple recessional moraines which were previously unmapped. The second site (ele. ~2800 m), located approximately 25 km west of Creede, CO, contains many large glaciated valleys with terminal moraines tens of meters in height. Both sites contain at least four terrace sequences. Previous research yielded terrace ages from three low-order tributaries of the Rio Grande, none of which are older than ~3300 cal yr BP. Research methods involved field mapping of moraines and terraces, profiling and laboratory analysis of soils, and the integration of georeferenced digital maps including soil descriptions. Future research plans include obtaining ¹⁴C and OSL ages in order to gain temporal control between moraine and terrace development, and correlating these ages with those of previous studies.