be difficult to reconstruct. For instance, Devils Tower in Wyoming and Needle Rock in Colorado were both thought to be volcanic necks, but further study has suggested they are eroded laccoliths. At Devils Tower, intrusion would have had to cool very slowly so as to form the slender pencil-shaped columns of phonolite porphyry seen today. However, erosion has stripped away the overlying and surrounding rock, so it is impossible to reconstruct the original shape of the igneous intrusion, which may or may not be the remnant of a laccolith. At other localities, such as in the Henry Mountains and other isolated mountain ranges of the Colorado Plateau, some intrusions demonstrably have the classic shapes of laccoliths. Extraterrestrial laccoliths There are many examples of possible laccoliths on the surface of the Moon. Some are centered in impact craters and may form as part of the post-impact evolution of the crater. Others are located along possible faults or fissures. Laccoliths on the Moon are much wider but less thick than those on Earth, due to the Moon's lower gravity and more fluid magmatism. Possible laccoliths have also been identified on Mars, in western Arcadia Planitia. Gallery See also References Further reading External links Petrology Igneous rocks Sheet intrusions Geologic domes Volcanic landforms