CHARACTERIZATION OF THE AGES OF SEDIMENT IN STINKING WATER CREEK, RIO BLANCO COUNTY, COLORADO, 2020-2021: INFORMATION ABOUT THE TIMING OF ARROYO CUTTING RELATIVE TO PERIODS OF LAND-USE CHANGE USING LUMINESCENCE

The Cretaceous Mancos Shale is a natural source of sediment, salinity, and selenium in western Colorado, and anthropogenic disturbances on Mancos Shale landscapes can expose and mobilize those constituents, leading to increased concentrations in surface water. Stinking Water Creek is an arroyo and a tributary to the White River near Rangely, Colorado. The basin, which overlies Mancos Shale, experienced land-use change in the 1800s and 1900s with the introduction of grazing and oil and gas development. Continued development of oil and gas resources has the potential to increase landscape disturbances and alter water quality. Understanding the effects of past land-use change could help resource managers to prepare for increased landscape disturbance that might occur in the future.

The U.S. Geological Survey used optically stimulated luminescence (OSL) and radiometric dating techniques to characterize the ages of sediment in Stinking Water Creek and provide information about the timing of arroyo cutting relative to periods of land-use change. In general, the ages of OSL samples from Stinking Water Creek fall into five broad categories: 8.5-8 thousand years ago (ka), 4.7-4.5 ka, 3.8-3.1 ka, 2.0-1.6 ka, 1.2-0.91 ka, and 0.73- 0.68 ka. One date that reflects a younger deposit (160 ± 10 years) was obtained in a previous study of headwater subbasins of Stinking Water Creek. Although no other modern deposits were identified, the results of this study help to characterize the geomorphic history of Stinking Water Creek. The OSL results provide evidence of multiple cycles of cutting and filling, similar to other arroyos in the Southwestern United States. Given the existing OSL dataset and the lack of data on past streamflow and loads, it is not possible to attribute portions of erosion in the Stinking Water Creek basin to time periods with intense grazing and energy development. However, this study nonetheless provides an important keystone site for future arroyo studies.