The Colorado Plateau of the Western U.S. harbors one of the most extensive exposures of Jurassic strata on our planet. Stretching from 200 to 135 million years ago, the Jurassic Period covered the heart of the Mesozoic Era, the Age of Dinosaurs.
A number of our National Parks and Monuments are famous for their Jurassic deposits and, by extension, their cargo of dinosaur fossils. Dinosaur National Monument, in northwest Colorado and northeast Utah, is a showcase for the Morrison Formation; deposited in a long, shallow basin, from Canada to New Mexico, this layer cake of mudstones, siltstones, coal and sandstone is famous for its late Jurassic fossils. A bit older, the Entrada Sandstone, deposited in the mid Jurassic, is highlighted at Arches National Park, in eastern Utah, where it has been sculpted into a spectacular array of fins, natural bridges and arch formations.
Perhaps most famous of the Jurassic sedimentary rocks is the Navajo Sandstone, deposited about 190 million years ago when a vast desert covered the region. Relatively soft and heavily jointed, this sandstone forms the upper cliffs of Canyonlands National Park, the scenic domes of Capitol Reef National Park and the towering walls of Glen Canyon, now drowned by Lake Powell. Separated from the Navajo Sandstone by the Kayenta Formation, the Wingate Sandstone yields the middle cliffs of Canyonlands and the majestic, sheer walls of Colorado National Monument; though officially dated from the onset of the Jurassic, some geologists argue that, based on its fossil contents, the Wingate was deposited near the end of the Triassic.
