For more than a century, the rocks of this region have attracted geologists and other scientists seeking to better understand Earth history. Notable pioneers such as John Wesley Powell, Clarence Dutton, Charles Walcott, Karl Gilbert and Herbert Gregory were among the first. Today, scientists build upon their legacy, discovering more and more every year in this vast outdoor laboratory.
The rocks tell of great mountain-building events and environments that were very different from those seen here today -- seas that have come and gone, great deserts, lush coastal swamps, forested uplands, and glacier-capped mountains. Many of the rock layers were deposited in low-lying coastal and marine environments that were situated much closer to the equator. Today’s landscape is in a state of erosion rather than deposition, largely because layers that were originally deposited near sea level have been pushed up to an elevation of greater than one mile. As the rock layers have risen, wind, water, and ice continue to erode the layers into the plateaus, canyons, and hoodoos that form today's magnificent scenery.
The rocks reveal a vast story that covers over 250 million years of geologic history. They are primarily sedimentary in origin and were laid down mostly during the Mesozoic Era. In some areas to the north, early Cenozoic Era volcanism emplaced igneous intrusions, and deposited lava flows and volcanic ash. The youngest geologic deposits in the field office area are alluvial sands and gravels that cover much of the region and give us clues about today’s eroding landscape.
A few of the past environments that are recorded in the rocks are listed below:
~ 270 million years ago
A shallow sea covered this region, depositing limestone and gypsum of the Kaibab Formation. During this period the region lie very near the equator, and the environment probably was very similar to what you find in the Caribbean today.
~ 210 million years ago
River systems originating from the Appalachian Mountains drained across the western interior, depositing the Chinle Formation. Great conifer forests covered the region, and tell-tale remnants can be seen today preserved as petrified wood.
~ 190 million years ago
A great desert covered what is now parts of Nevada, Arizona, Utah, Colorado and Wyoming. Sands eroded from the Appalachian Mountains were carried to the northwest by large trunk rivers and then blown to the south by strong seasonal winds. In this area, these fossilized dunes are known as the Navajo Sandstone. The Navajo Sandstone makes up one of the five "risers" in the Grand Staircase. A good analogy today for what this region was like 190 million years ago is the Sahara Desert in Africa.
~ 93 million years ago
This was a time when there were no polar icecaps and sea level was at its highest recorded level. An interior basin was developing due to mountain building in the west, creating a great inland seaway that would cover much of what is now the central United States. Fine-grained sediments accumulated on the sea floor, later to become what is known as the Tropic Shale.
~ 25 million years ago
About this time signaled the start of Basin and Range extension and a period of extreme volcanic activity. Cataclysmic eruptions occurred, depositing thick welded tuffs and other igneous deposits throughout the region. Volcanism continued up until about 100,000 years ago. Basin and Range lowering to the south and west is thought to be the primary mechanism for the sculpting and erosion of the landscape we see today. Many of the National Parks and Monuments in the region were established thanks to the fabulous visual scenery that is exposed throughout this geologic landscape.
Major mountain building (tectonic) events affecting this region:
140 to 50 million years ago – Sevier orogeny
80 to 35 million years ago – Laramide orogeny
25 million years ago to present day – Basin and Range extension
Utah Geological Survey
Online Geologic Maps
Sedimentary Rocks on the Colorado Plateau
Geologic Time Chart
Grand Staircase-Escalante National Monument (GSENM) Geology Page