Willow Mountain is a 3,826-foot volcanic summit in the Christmas Mountains of far West Texas that rises sharply above nearby Highway 118, making it a prominent landmark in the Chihuahuan Desert. Formed about 43 million years ago as an intrusive plug, it was exposed as surrounding rock eroded away. Cooling and contraction created regular joints, and later weathering revealed them, especially on the west face, where striking columns make the mountain one of the southern Big Bend area’s best displays of rock jointing. Its runoff ultimately reaches the Rio Grande, and its name, used since at least 1904, may derive from nearby Willow Spring.