Today is the second day of talks at the annual meeting of the Geological Society of America in Denver, where I currently am. The morning session I'm attending is about the newest research related to the Grand Canyon, specifically the country below the mouth of the canyon from Las Vegas down to the Gulf of California. Recent mapping has been revolutionizing our understanding of the area, with the new favorite hypothesis being an invasion of the Colorado River from the brand-new canyon that quickly filled a series of large lakes separated by natural dams. As the lake highest upstream filled with sediment, clear water spilled over its dam to fill the next lower basin, where freshwater limestone was deposited. Once the higher lake filled in, the river cut down the dam and started filling the next lower basin with sediment. This series involved seven separate basins and took just a few hundred thousand years, which is fast enough to get geologists' hearts racing. The field photos from the desert are beautiful and the audience is fully engaged. That's the kind of thing I treasure.