Geological Survey John Wesley Powell's Exploration of the Colorado River

The largest, deepest, and most spectacular canyon through which the river flows is the Grand Canyon in northern Arizona, 217 miles long and from 14 to 18 miles wide. The south rim of the canyon is 7,000 feet above sea level and nearly 1 mile above the canyon floor. The north rim is 8,200 feet above sea level and averages more than 1 mile above the canyon floor.

The Colorado River at a point little changed since Powell's voyage in 1869.

The Grand Canyon has been carved by the Colorado River and its tributary streams, which have carried downriver the rocks and soil supplied to them by the weathering and breaking up of the canyon walls, and at the same time, have cut their own channels deep into the solid rock. Some geologists believe that it is geologically young, not more than a few million years old; others contend that it has been carved out by the river over a much longer period, perhaps several tens of millions of years.

The river itself has cut only a narrow slot. The great width of the Grand Canyon is the result of erosion by landslides, runoff of water from the sides, ice and frost action, and other wearing agents.

In cutting the chasm, the Colorado River has exposed a great series of rock layers. Fine examples of the rocks of all known eras of geologic time (from the Precambrian to the Cenozoic) may be seen, recording a span of nearly 2 billion years. In these rock layers are fossil remnants of prehistoric life ranging from primitive sea plants to early kinds of land life such as ferns and lizardlike reptiles.

". . . the canyons of this region would be a Book of Revelations in the rock-leaved Bible of geology." —John Wesley Powell

The earliest known settlers in the Colorado basin were a prehistoric people called Hohokan, who lived and vanished in the Salt River Valley before the Hopi and Pueblo Indians inhabited the area. The Papago Indians are probably their descendants. The ancestors of the Apache and Navajo Indians came in the 13th century.

Probably the first European to see the Colorado River was Francisco de Ulloa, a Spanish soldier and explorer, who reached the head of the Gulf of California in his search for the famed Seven Cities of Cibola in 1536. The first Europeans to view the Grand Canyon were Captain Garcia Lopez de Cardenas and 12 soldiers, who in 1540 were sent by Francisco Vasquez de Coronado, Spanish explorer of the Southwest, to verify Indian tales of "a great river and chasm."

Father Eusebio Kino, a Jesuit priest, established missions in Arizona at San Xavier de Bac in 1700 and at Gueravi in 1732. The first European settlement was established near present-day Tucson, Arizona in 1776.

Navajo boy (left), Tusayan maskette (middle), Navajo guide (right).