Great Plains Geology (MP-124) Diffendal Jr., R.F. 2017 210pp, size 8" x 5". Description: Great Plains Geology concisely guides readers through the geological development of the Great Plains region. It describes the distinct features of fifty-seven geologic sites, including fascinating places such as Raton Pass in Colorado and New Mexico, the Missouri Breaks of Montana, and the Ashfall Fossil Beds in Nebraska. This guide addresses the tricky question of what constitutes the Great Plains, showing that the region is defined in part through its unique geologic features.