_Geologic History._--A large part of geologic history is revealed in the canyon walls of Zion and Bryce Canyon National Parks. Just as Grand Canyon is the best known record of ancient geologic history, Zion Canyon records most clearly the events of medieval geological time, and Bryce reveals much of modern geologic history. The story of Zion begins where that of Grand Canyon ends, and ends where Bryce begins. The rocks exposed in these three national parks incorporate the records of a billion years.
[Illustration: _Generalized section of sediments in Zion and Bryce Canyons_]
lava Eocene Wasatch: Pink Cliffs ROCKS IN BRYCE CANYON PARK MESOZOIC Cretaceous Undifferentiated: Gray Cliffs sandstone shale coal Jurassic gypsum Carmel limestone Navajo sandstone: cross-bedded ROCKS IN ZION PARK White Cliffs sandstone Kayenta-Wingate Triassic Chinle: Vermilion shale, Cliffs sandstone, ash and limestone fossil wood Shinarump conglomerate Moenkopi: Belted shale Cliffs sandstone oil RIM OF GRAND CANYON Permian Kaibab limestone
A study of the rocks of Zion and Bryce Canyon shows that during the last 200,000,000 years the region comprising the parks has witnessed many changes in landscape and climate. At times it was covered by the sea, at other times broad rivers traversed its surface, and at still other times it was swept by desert winds. Most of the rocks were laid down by water as gravel, sand, mud, and limy ooze. They have been converted into solid rock by the weight of layers above them and by lime, silica, and the iron that cement their grains. Embedded in the rocks are fossil sea shells, fish, trees, snails, and the bones and tracks of land animals that sought their food on flood plains, in forests, or among sand dunes. The most conspicuous remains are those of dinosaurs--huge reptiles that so dominated the life of their time that the Mesozoic is known as the "age of dinosaurs."
The accumulation of some 8,000 feet of strata (Mesozoic and Tertiary) on top of 4,000 feet of older (Paleozoic) beds, which are exposed in Grand Canyon, may be considered the first of three major events in the development of the marvelous landscapes of the Zion-Bryce region; it provided the material from which the huge scenic features were later carved. The second event was a regional uplift which elevated the previously low-lying top beds of the series (Wasatch, Pink Cliffs) to a height of nearly 2 miles above sea level. As a result of this movement, the earth's crust was broken into huge rectangular blocks by north-south fractures or faults. Three of these great faults can be seen in the vicinity of the parks: the Hurricane fault in the Hurricane Cliffs, west of Zion; the Paunsaugunt fault in the cliffs of Bryce; and the Sevier fault along the Mount Carmel Road between the two parks.