>when no one is around
Just wait long enough and people will walk out of the frame. Pic related is a snapshit at Delicate Arch with no one in it but there were people all over the place, I just waited until people finished taking their pictures underneath it. Just be patient, or better yet, go somewhere less crowded (for example, skip Arches and go to Canyonlands instead, or if you want to shoot the Grand Canyon do it outside of the summer).
