Arizona, United States
El Capitan, also called Agathla by the Navajo people, is a peak south of Monument Valley, Arizona, over 1500 feet (457 meters) high. It is a few miles north of Kayenta and is visible from State Highway 163. Agathla is derived from the Navajo Indian word 'ag ha la' meaning 'much wool', apparently for the fur of antelope and deer accumulating on the rock. It is considered sacred by the Navajo.
El Capitan is an eroded volcanic plug consisting of volcanic breccia cut by dikes of an unusual igneous rock called minette. It is one of many such volcanic diatremes that are found in Navajo country of northeast Arizona and northwest New Mexico. El Capitan and Shiprock in New Mexico are the most prominent. These rocks are part of the Navajo Volcanic Field, in the southern Colorado Plateau. Ages of these minettes and associated more unusual igneous rocks cluster near 25 million years.