May 01, 2011
Bryce Canyon (1)
Bryce Canyon (2)
Bryce Canyon (3)
▪ The Bryce Canyon area shows a record of deposition that spans from the last part of the Cretaceous period and the first half of the Cenozoic era. The ancient depositional environment of the region around what is now the park varied. The Dakota Sandstone and the Tropic Shale were deposited in the warm, shallow waters of the advancing and retreating Cretaceous Seaway (outcrops of these rocks are found just outside park borders). The colorful Claron Formation, from which the park's delicate hoodoos are carved, was laid down as sediments in a system of cool streams and lakes that existed from 63 to about 40 million years ago (from the Paleocene to the Eocene epochs). Different sediment types were laid down as the lakes deepened and became shallow and as the shoreline and river deltas migrated.
▪ Several other formations were also created but were mostly eroded away following two major periods of uplift. The Laramide orogeny affected the entire western part of what would become North America starting about 70 million to 50 million years ago. This event helped to build the ancestral Rocky Mountains and in the process closed the Cretaceous Seaway. The Straight Cliffs, Wahweap, and Kaiparowits formations were victims of this uplift. The Colorado Plateaus were uplifted 16 million years ago and were segmented into different plateaus—each separated from its neighbors by faults and each having its own uplift rate. The Boat Mesa Conglomerate and the Sevier River Formation were removed by erosion following this uplift.
▪ Vertical joints were created by this uplift, which were eventually (and still are) preferentially eroded. The easily eroded Pink Cliffs of the Claron Formation responded by forming freestanding pinnacles in badlands called hoodoos, while the more resistant White Cliffs formed monoliths. The brown, pink and red colors are from hematite (iron oxide; Fe2O3); the yellows from limonite (FeO(OH)·nH2O); and the purples are from pyrolusite (MnO2). Also created were arches, natural bridges, walls, and windows. Hoodoos are composed of soft sedimentary rock and are topped by a piece of harder, less easily eroded stone that protects the column from the elements. Bryce Canyon has one of the highest concentrations of hoodoos of any place on Earth.
▪ The formations exposed in the area of the park are part of the Grand Staircase. The oldest members of this supersequence of rock units are exposed in the Grand Canyon, the intermediate ones in Zion National Park, and its youngest parts are laid bare in Bryce Canyon area. A small amount of overlap occurs in and around each park.