of deserts has marked the geologic history of Arizona. Landscapes that we see today are here because of landscapes of the past, and because of tremendous forces deep within the earth, forces that carry continents into collisions and then drag them apart again, forces of heat and pressure and the slow churning boil of the earth's interior. Landscape features result, too, from more comprehensible, more recent forces: the unending attack of water and wind and frost, the building of volcanoes, the short-term geologic happenings like landslides and rockfalls, earthquakes and floods, and a gopher digging a hole.