 Some natural bridges may look like arches, but they form in the path of streams that wear away and penetrate the rock.Pothole arches form by chemical weathering as water collects in natural depressions and eventually cuts through to the layer below.Natural Bridges National Monument in Utah protects the area surrounding three large natural bridges, all of which were formed by streams running through canyons, the largest of which is named Sipapu Bridge with a span of .