The Painted Desert extends over 7,500 square miles across northeastern Arizona, and because Petrified Forest National Park lies at its heart, the entire park contains the Painted Desert’s colorful rocks. These mudstone and sandstone rocks, called the Chinle Formation, were deposited from 227 to 205 million years ago during the Late Triassic Period, when the supercontinent Pangaea broke apart and eventually formed the present continents. Over the next 180 million years, the rocks of the Chinle Formation were deeply buried, uplifted, and eroded into the badland topography seen today. Approximately 20 million years of Late Triassic rock and fossil history are recorded in this geologic kaleidoscope.