There are three publicly-documented sites in Fish Slough outside of Bishop, CA that contain petroglyphs described by a BLM brochure. All of these pictures were taken at one of those three sites.
Petroglyphs are created by chipping away the desert varnish (or patina) of the volcanic rock to reveal the lighter rock beneath the surface. As the years pass by, the lighter rock oxidizes and the desert varnish reappears. By nature, petroglyphs are ephemeral. Be a good steward of the land, and don't hasten the passage of time. Eventually, the petroglyphs will disappear; please, do nothing that will speed the process.
As the petroglyphs age, they darken and begin to fade into the remaining desert patina. In order, to highlight the petroglyphs, many of the photographs have been over-processed, contrast is increased and color saturation has been modified.