Devils Postpile National Monument is located near Mammoth Mountain in eastern California. The national monument protects Devils Postpile, an unusual rock formation of columnar basalt. Devils Postpile National Monument encompasses 798 acres (323 ha) and includes two main tourist attractions: the Devils Postpile formation and Rainbow Falls, a waterfall on the Middle Fork of the San Joaquin River. In addition, the John Muir Trail and Pacific Crest Trail merge into one trail as they pass through the monument. Excluding a small developed area containing the monument headquarters, visitor center and a campground; the National Monument lies within the borders of the Ansel Adams Wilderness.