Canyon was formed over millions of years as tectonic movement forced the Colorado River to forge a new route before it emptied into present day Gulf of California. Erosion, weathering, and climate played a major role in carving the canyon we see today. These processes allow us to see the rock layers, or strata, that provide a window into the past. Most of the layers are comprised of sedimentary rock as the Colorado and its tributaries deposited some of its contents on its way to the sea. Over time, these contents hardened and have become the soft shale and limestone of today.

The geology of Grand Canyon provides an exceptional window through which to view three of the four major eras of geological time through its various strata and its immense fossil record. Grand Canyon averages 4,000 feet deep throughout its 277 mile length with astounding 6,000 feet depth at its deepest point. Its width averages around 11 miles wide with a 15 mile diameter at its widest point. Among the fossils discovered at Grand Canyon are bacteria spores over one billion years old, body fossils that date to the Paleozoic era (550-250 million years ago) and mummified hair and dung from over 11,000 years ago.

Grand Canyon is home to an estimated 1,000 caves, many of which have not been catalogued. It is also home to many faults. What makes Grand Canyon unique is that along with faults contained horizontally on the surface of the canyon, there are a number of vertical faults as well. These faults are important because they allow seismologists and other scientists an opportunity to study them as they descend thousands of feet into the earth’s top layer, the crust. The faults span each of the geologic periods of time, spanning millions of years into the earth’s history.

Because Grand Canyon acts as a gateway into the earth’s history, geologic study has been abundant, starting in 1858. Grand Canyon and the region lend themselves to the study of stream erosion and volcanism. Two billion years of history are on display via the cross section of rock present within the canyon walls. Sediments and lava flows crystallized into granite during the late Precambrian Era. This granite fused to the North American continent. Most of what is seen in Grand Canyon comes from the Paleozoic Era. Marine and coastal environments withdrew between 550-250 million years ago leaving shale, sandstone, and limestone behind with thickness reaching up to 5,000 feet. Most recently are deposits from lava flows from the time of Dinosaurs. Volcanic activity that began some six million years ago has extended until as recently as a few thousand years ago. (See Sunset Crater)

Grand Canyon’s formation mostly hails from the Cenozoic Era when snow melts fueling the Colorado River carved the canyon downward. The region’s arid climate prevents the hastening of widening of Grand Canyon and the forces of widening and downward carving provide the canyon rather than a more common river valley. Aridity in the region provides the exposed rock rather than abundant plant growth. All of this allows for some 40 rock layers which can be studied individually as the geologic history of each era they represent. While Grand Canyon supplies many answers to geologic history questions, many still remain and scientists are far from finished their study of the canyon and the region.

The Colorado River is the most important source of Grand Canyon’s formation. Its flow, which begins in the Rocky Mountains and is aided by its tributaries, provides the most important source of water in the region. Springs and seeps also contribute to the water flow of the Colorado, although only slightly. Nevertheless, springs are important in that they are home to diverse environments where scientists have discovered species of wildlife found no where else in the world.