I don't know about any guided tours or the companies that offer them, but there are a lot of great rides around here.
The southern Utah area is full of good rides as well, and tourism being one of their major industries now, I would think there are some bike tours around.
If you just want rent a bike and take a couple day rides, let me know. I'll see if my schedule can open up. It's getting about time for some Death Valley rides, always fun.
