Did the Colorado River Once Run North from Grand Canyon to Montana? Geologic Field Evidence in the Swan River Valley - Pocatello Area of Idaho

• Main Authors: Burke, Siobhan, Bazo, Wayne, White, Michael, Parker, Stuart
• Format: Text
• Language: unknown
• Published: ScholarWorks at University of Montana 2015
• Subjects: Labrador Sea
• Online Access: https://scholarworks.umt.edu/umcur/2015/poster_1/14

The Colorado River did not always run south into the Gulf of California. Studies suggest it may have once flowed north through Idaho and Montana before discharging into the Labrador Sea. During past geologic periods, the river’s path may have taken it through the Swan River Valley-Pocatello area of SE Idaho. Research into this area indicates that it was possibly the site of an ancient riverbed. Did it flow north, as predicted by recent studies? The area underwent large-scale geologic changes through glacial processes, faulting, volcanism, and uplift, causing drainages to shift their courses. In the study area, the bed of the old river valley may have eroded deep into Cambrian and Precambrian quartzites. If exotic quartzite cobbles stranded on high mountain passes in SW Montana were derived from bedrock in the study area, the river must have run north. Over the semester, this project will analyze the geologic history of the study area through analysis which includes literature review, field observations, petrologic analysis, structural interpretation, field measurements of geologic formations, and the GPS co-ordinates of the field sites. A map of the area will be created along with a cross-section of the subsurface geology. By conducting this research we intend to establish if the study area contains the deeply eroded bed of the old north-flowing river. We hope to date remnants of the old river deposits near Pocatello and Swan River Valley, and determine ancient flow directions from field observations. Geology of this area has been studied and mapped extensively. However, the concept of regional tectonics influencing the course of the proposed north-flowing river is a hypothesis that has not been considered. This will contribute to our understanding of tectonic impacts on river systems and help identify possible untapped ground water resources in semi-arid areas.