ELEVATION, LONGITUDINAL PROFILE, AND SCHMIDT HAMMER ANALYSIS OF STRATH TERRACES THROUGH CAPITOL REEF NATIONAL PARK, UTAH: BEDROCK CHANNEL RESPONSE TO CLIMATE FORCING?

Elevation, longitudinal profile, and Schmidt hammer data indicate that strath terraces (specifically the lower elevation terraces) mapped in the Fremont River drainage of Capitol Reef National Park are correlative to the terraces of the smaller Pleasant Creek drainage located approximately ten miles to the south. This correlation suggests that drainage development in this area of the Colorado Plateau was strongly dependent upon a regional-scale forcing mechanism (e.g. climate) rather than independent basin-scale processes.

Elevations of mapped strath terraces and their associated black volcanic boulder deposits were calculated from geologic maps, Digital Elevation Models (DEM), and Digital Orthophoto Quadrangles of the Fruita and Golden Throne 7 ½' Quadrangles, Wayne and Garfield Counties, Utah. Terraces in both drainages were placed into twenty foot elevation bins and then gathered into larger terrace levels based upon population breaks and the degree of weathering as seen from Schmidt hammer hardness data. Associated terraces from both drainages were then compiled into longitudinal profiles to illustrate past down-cutting events. Comparison of the two datasets indicate that the two lowest terrace levels of the Fremont River compare well with the two terrace levels of Pleasant Creek both in elevation above the present stream bed and in Schmidt hammer hardness measurements.

Our data demonstrate that the Fremont River drainage is likely much older than the smaller Pleasant Creek drainage. Further, correlative terrace data strongly suggests that glacial-interglacial climate forcing played a dominant role in the landscape evolution of both drainages and by inference, the broader Colorado Plateau. Lastly, terrace elevation data were compared with recently published cosmogenic ages for several terrace deposits located within the Fremont River drainage. This comparison provides compelling evidence that highest concentrations of preserved terraces may be time correlative with discrete isotopic stages associated with glacial maximum conditions.