English: The 41,170 acre Bisti/De-Na-Zin Wilderness Area, a rolling landscape of badlands offering some of the most unusual scenery found in the Four Corners Region, is a veritable hot bed of fossil discovery. The Wilderness Area is composed of formations of interbedded sandstone, shale, mudstone, coal, and silt. Paleontologists have studied and researched this area for nearly a century. The Badlands feature an exposure of rocks known as the Fruitland/Kirtland Formations that represent a time near the end of the Cretaceous Period (approximately 75 to 80 million years ago). These continental sediments chronicle the time near the end of the Age of Dinosaurs. This sequence of rock formations is one of only four known in the world that record this transition, and may help explain why the dinosaurs became extinct. One of the more interesting dinosaurs found in the Wilderness Area was the remains of a large carnivorous dinosaur which was named Bistahieversor sealeyi - affectionately known as the Bisti Beast. This 30-foot tyrannosaur roamed the Earth around 74 million years ago and so far has only been found in the State of New Mexico.