In Big Bend’s Boquillas Formation, Geologists Trace an Ancient Chapter in Earth’s History

Visible in the park’s southeastern corner, near the hot springs and Boquillas Canyon, the Boquillas Formation is a series of limestones and shales, in white, tan, yellow and brown. These rocks were laid down in shallow ocean waters across 10 million years, and they abound in fossils, which capture the emergence and extinction of countless creatures.