Petroglyphs at Grimes Point. Prehistoric natives drew petroglyphs in boulders of andesite lava flows along the shores of the ancient Lake Lahontan. The boulders are coated with rock varnish, a thin layer of dark brown to black iron and manganese oxides. The U.S. Bureau of Land Management has constructed a path along which you can view the petroglyphs. Do not disturb the petroglyphs or collect rocks at this site.