Devils Tower National Monument
Detailed Description
This view shows the large rubble blocks that make up the talus apron around the base of Devils Tower. The tower consists of mostly a dark igneous rock called phonolite, being coarsely porphyritic (bearing crystals including both mafic and feldspar minerals) in a fine (aphanitic) olive-gray groundmass. Much of it has a welded breccia texture (Karner and Halvorson, 1987).
Sources/Usage
Public Domain.