Mule Ear Peaks are twin summits in the Chisos Mountains of Big Bend National Park in Brewster County, Texas, rising prominently from the Chihuahuan Desert as one of the park’s best-known landmarks. Nearly equal in height, their spires tower steeply above Smoky Creek and drain toward the Rio Grande. They are the exposed remains of a rhyolite dike formed about 29 million years ago during the Oligocene, with nearby rock layers reflecting the area’s volcanic past. Long known by their descriptive name, the peaks also figured in Army Air Corps flight training in the 1930s and in climbing history with a recorded ascent in the 1940s.