One thing to note. When the Long Valley people's built places like Mesa Verde the environment was rather different-it was a dry forest largely as shown with Strontium Isotopes of support beams and Pack Rat midden studies. Jared Diamond's book Collapse has a good breakdown of this and the distinction that allowed the related/decendent culture of the Puebo peoples to thrive in its place (decentralization mostly).

Yes soft good would survive (although be rare) - also where streams reach the valley there would be more waterfalls of the type you originally mentioned. Also remember that much of the valley floor was given over to farming.