Geologist, guide, and writer Wayne Ranney is blogging from the Colorado River origins & evolution workshop in Flagstaff with some in-depth and insightful descriptions of the debates at his blog Earthly Musings. [right, regional map posted by Kyle House]
I won't try to summarize them here. You need to read Wayne's posts. The workshop continues through today. Abstracts and data files are posted on the workshop web site.