Willow Mountain, Texas, USA
U.S. Geological Survey photo by R. L. Brown. (fair use policy)
Willow Mountain is part of Big Bend National Park, in southwestern Texas. Like many peaks in the Big Bend region, it has a volcanic origin, but it's distinctive for its display of columnar jointing.
Jointing happens to rocks in many different settings, but when a thick body of magma cools slowly underground, it contracts and splits into pencil-shaped columns. The cliffs of the Palisades, across the Hudson River from New York City, are another famous example, as are Devils Postpile National Monument in California and Giant's Causeway in Ireland.
