Well, I live in Southern AZ which is nothing but desert (or do I need a second s?) and rocks.... and well cactus. Anyhow, when I take them out to trail ride we get down into 3 different wash area which is nothing but sand & rocks (somewhat like beachy sand - where they sink in a lil). Well, my horses are barefoot, and so are my friends. Infact, we even let them full out gallop them in it. They do great! I would just suggest taking a hoof pick, that way if a rock gets lodged. I think the longest we've gone on was a 3 hour.
Don't know if that helps any.