Watercolor… Bryce Canyon Natural Bridge, Utah… color sketch (plein air) on site July, 2006. Limestone, siltstone, dolomite and mudstone erode over very different amounts of time. And this process, that is responsible for all of these hoodoos, arches, ravines, washouts and whatever else is out there… has been going on for more than 60 million years. You ought to go there and see this place for yourself.