Figure 4.
Miocene central-western United States drainage. Upper Colorado River basin (cross-hatched) drains structural trough toward southwest corner of Colorado Plateau, leading to rift systems through Nevada, Idaho, and Montana, to headwaters of South Saskatchewan River. Antler orogenic belt, Cambrian-Precambrian Z (
Z) quartzite, Lemhi Group, and Belt Supergroup bedrock sources feed gravel northeast along Miocene river. CCR—Crooked Ridge River; GC—Grand Canyon; GF—Great Falls; K—Kaibab Upwarp; LCR—Little Colorado River; UMR—Upper Missouri River; black—Caliente caldera complex; dotted, inverted Vs—uplifts on west flank of Miocene river. Dashed gray line—Yellowstone hotspot track. Note that northern part of upper Colorado River basin was not integrated with southern part until late Miocene (Cather et al., 2012).