I think I can help you out with that, the tribe around the Colorado River that comes to mind is the Navajo, but they're not the only ones, there are also the Mohave and the Havasupai, however, the one that's most commonly associated with the Colorado River is probably the Mohave, they've been living along the river for centuries and have a deep connection to the land and the water, so that might be the answer you're looking for.