Less than 100,000 years ago, basalt lava erupted in the already glaciated valley of the Middle Fork of the San Joaquin River.

Columnar joints or cracks are formed as the lava flow cools and shrinks.

The surface of a homogeneous medium, when subjected to uniform shrinkage, is divided into cracks defining regular hexagons.

A hike to the top of the Postpile reveals the polished tops of the rock columns, exposed like a tiled floor.

Columns have an average width of 2 ft; some are 60 ft long.

History --

• Devils Postpile was once part of Yosemite National Park

• Discovery of gold near Mammoth Lakes prompted a boundary change that left the Postpile on adjacent public land

• A proposal to build a hydroelectric dam later called for blasting the Postpile into the river

• Influential Californians, including the renowned civil engineer Walter L. Huber, persuaded the federal government to stop the demolition

• On July 6, 1911, President William Howard Taft signed the proclamation creating the Devils Postpile National Monument

Text:  Victor M. Ponce

Music:  Benedetti & Sbovoda

Editor:  Flor Pérez

Credits:  N. King Huber (USGS)

               W. W. Eckhardt (NPS)