Spill-over theory of Grand Canyon origin

 The Rock Whacker blog recently took a lengthy examination of the origin of the Grand Canyon [right, credit: NPS], concluding that the 'spill-over theory' is the best explanation:

"...rivers from mountains to the east of the Grand Canyon poured water into a giant basin, larger than Lake Michigan today. Once the water reached the top of the western rim of the lake, it spilled over onto the plateau where the Grand Canyon currently is."