With those two pictures being so near-identical, another fairly easy method you could use would be to copy the photo with the man as a new layer over the other pic, do a quick alignment using the 'difference' blend mode, then erase away the man from the top layer letting the rock from the other layer show through. I did a quickie in 30-40 seconds using your small posted version and it worked like a charm. The two pics are only off by a few mm, so they are very simple to align.
Tim's advice is great - I love clone brush, and use it all the time. I usually use a nice small sample size (10-30) depending on the size of the pic, and unless it is a uniform color, I sample a few times from different places in the photo. Also, when cloning stuff with a very busy pattern (sand, leaves, etc) you can reduce the opacity of the clone brush for a second or third pass, to run over seam lines or areas that are two opposing colors, to help them blend better, so the cloned area doesn't stand out.