Thursday, August 15, 2013
USGS.gov, Geological Survey Bulletin 1393, The Geologic Story of Arches National Park. When a similar rock structure does not span a eroded canyon or valley, it is called an "arch." The term "window" is somewhat arbitrary. In this case, the Angel's Window on the North Rim of the Grand Canyon, is somewhat overwhelmed by the size of the cliffs and the surrounding canyon. It is barely visible near the top of the jutting ridge. Usually, shots of Angel's Window give the impression that it a huge structure. It is large, but not so large as to be very visible unless you are right next to it. Sometimes the designation "window" is used when the arch is more like a hole in the rock face than an actual arching structure. There are lots of unnamed windows in rocks around Arizona.