i appologise in advance if this is a duplicate but i have read through all the pages i can with out going blind, i have heard that it is possible to get on the bridge on desert gulch, i have never seen this my self and have read through most of if not all of the forums and each one has different info on what to do. i do know of a few glitchs myself if anybody wants to swap.
You bet its a duplicate thread, try going to page 4, there's 3 threads on this on that page.
Also, as far as I know there is no Desert Gultch glitch. I have never seen it done, never met anyone who has ever seen it, never met anyone who has known how to do it, and never even seen a screenshot of anyone on the bridge. So the answer is likely, "no" it does not exist and its 100% myth made up by some child.