Yeah, there's lots of camping, sometimes free in the West. I'd recommend stopping in the Boulder/Denver area on the way to Moab. There are tons of XC trails there. Crested Butte is a little out of the way, so I'd suggest just driving the 5 hours from Denver to Moab. Moab might be a bit hot this time of year, but it's a beautiful place so I'd go anyway. Take US50 (the so-called Loneliest Road in America) for an interesting driving experience and head to the Lake Tahoe area on the border of California/Nevada. Lots of good riding around there. You might want to try renting a downhill rig at Northstar just for the heck of it. After that it's only another 4 hours to Berkeley. There are a few decent trails in the Bay Area too.
The best part of the USA is from the Rocky Mountains to the Pacific - enjoy!