DEVILS POSTPILE NATIONAL MONUMENT

national monument in Madera county, east-central Calif., U.S., situated on the middle fork of the San Joaquin River. The formation consists of polygonal basaltic columns some 40 to 60 feet (12 to 18 m) tall and 10 to 30 inches (25 to 75 cm) in diameter. It was created some 900,000 years ago by the cooling and cracking of hot lava. Devils Postpile, which consists of 798 acres (323 hectares) of land, was proclaimed a national monument on July 6, 1911.