"This area of the Peruvian Coast is among the driest areas in the world. It often doesn't rain for years on end. The Mancos Valley, at least the upper portion, is a beautiful mountain valley with lots of trees and lush grass." Did you look at the pictures in the pdf file? Especially the one that overlooks the river valley, toward the cliffs and hills beyond.
The area looks a great deal like the Mancos Valley, as seen from the northern front of Mesa Verde.
Or, perhaps, the better perspective might be looking from the La Platas back across the Mancos toward Mesa Verde.
You're quite right. The areas look very similar. I was trying to point out that I believe the climate is dramatically different. I assume the Peruvian valley is irrigated or it would be as dead as the surface of the moon. The Mancos Valley, which I am very familiar with (used to live nearby), has a fairly heavy natural rainfall.