Devils Postpile National Monument, National Monument in Madera County, United States.

Devils Postpile National Monument is a protected area in Madera County, California, preserving a massive wall of hexagonal basalt columns. The structure rises along a slope, with each column running parallel to the next and forming a pattern that looks like tightly packed pencils.

President Taft declared the area a protected monument in 1911 after plans for a dam threatened the formation. Ice shaped the landscape during the last ice age and left behind the smooth surface on top of the columns.

Historic Spots in California (1966) records that sheep-herders saw Satan's handiwork in every scenic freak, so the formation was long known locally as the Devil's Woodpile. The name Devils Postpile, officially styled without the apostrophe since the 1930s, compares the columns to posts stacked in a pile. The John Muir Trail and Pacific Crest Trail merge into one route through the monument.

Visitors reach the area by shuttle bus during summer months when the access road is open. In winter, snowshoes or cross-country skis provide the only way to reach the columns, as no vehicles pass through.

A survey of 400 columns found 44.5% six-sided, 37.5% five-sided, 9.5% four-sided, 8.0% seven-sided and 0.5% three-sided. The Postpile also lacks the horizontal jointing seen at most other basalt-column sites, which is why the columns run as continuous posts.