| Tower Point Ruin was built overlooking the intersection of two tributary canyons of Little Ruins Canyon. Over time, gradual stream erosion and gravity-induced mass wasting undercut the cliffs, causing large blocks of the cap-rock sandstone to tumble into the canyon. Some of the surfaces of the blocks and cliff surfaces preserve dark streaks of desert varnish. Desert vanish is a thin, dominantly manganese mineral coating that forms on the surface of rock. Manganese-fixing bacteria living on the rock surface help trap minerals from atmospheric aerosols (clays, dust) and streaming water (Dorn and Oberlander, 1982; Garvey and others, 2008). Ancient carvings (pictographs) in the desert varnish slowly heal, showing that desert varnish layers build up slowly over hundreds or even thousands of years. |
