I live here in Co, and about the only places I know of with sand are Walden, Co which is going to be getting cold quickly due to it being around 8000' elevation. There's Little Sahara over in Utah....about 4 hours into Utah on 70. Its good sand dune riding but will be getting cold as well shortly. Check out www.duneguide.com. They have a good list of sand dunes to ride all over the states here.
We met an older couple riding this weekend and they were telling us they make yearly trips to Colorado and make a 460+ mile trip over what I thought he said was Elk Pass but I can't find anything about it. Any idea what he might have been talking about.
Oregon dunes look beautiful. Wish I was still there. I might have to check out central AZ "Prescott, Flagstaff area" I have a lot of family there. Colorado controls so much...