[dirtboy]

No mystery about it. The current Rockies (yes, there were ancestral ones) were uplifted 70 million years ago or so in the Laramide Orogeny. They were then eroded until they were a level plain with a few peaks poking up. Then the entire region was uplifted again, probably from the Yellowstone and Raton hot spots migrating underneath the region, and the eroded debris was transported away, leaving the eroded surface elevated. The best example of what this used to look like is the Gangplank in SE Wyoming, where the original erosional surface is still continuous to the top of the Laramie Mountains, a very convenient situation for the Union Pacific.

I've been to both the peneplains of the Wind River Range at 12,000 feet and the Gangplank.

[Natufian]

Thanks for that. I learnt more reading your post than I have from years of creationist ‘science’ articles.

[elteemike]

I had a geophysicist/geologist buddy clue me in to the natural history of the West, Utah and Colorado in particular, and the series of mountain building, erosion, shallow seas, dune deserts etc...I remember he said there have been 5 different cycles of this...Explains the brown, tan, pink layers in the sedimentary rock formations...

I now look at the drive across central Utah (San Rafael Swell, in particular) entirely differently...

Thanks for the post...

[fishtank]