water washed sandstone   Water washed sandstone is a dense, hard, finegrained, commonly feldspathic sandstone or siltstone of medium to dark gray or bluish-gray color. It has naturally rounded edges, with distinctive smoothness and colors. Centuries of moving glacial waters and shifting streambeds created this beautiful rock. It was then transported by gravity, mudflows, or running water, and eventually deposited in various settings in desert dunes, creek beds, streams and continental shelves. san pablo tehama