The famous buttes of Monument Valley developed out of an interaction between two completely different types of sandstone. They are the remnants of an eroded plateau, called mesa. A small mesa is a butte. These are composed of hard and resistant sandstone from the Permian age. The lower stratum is composed of soft rock from sandy river sediments, that erode in 45° sloped alluvial fans.
Pentax K2, Pentax 50mm, f/8, 1sec, Kodak Ektachrome E6, ISO 100, tripod