Colorado River (37N, 118W US)

This image shows the Colorado River, the largest river in the southwestern United States, along with two of its tributary rivers, the San Juan and the Escalante. As the Colorado River flows through southern Utah, it continuously erodes through the sedimentary rock layers forming deep, narrow canyons. The tree-covered, high-elevation mountains around the head of the Escalante River basin appear dark compared to the sparsely vegetated, red-rock regions of the several smaller drainage systems found at lower elevations.

Navajo Mountain marks the gathering of the San Juan and Colorado rivers. This isolated dome volcano, easily visible as a dark circular mountain just off-center in the photograph, pushed up through the sedimentary rocks of the Colorado Plateau. It lies near the Utah-Arizona border and strongly contrasts with the red sandstone buttes and mesas that characterize the rest of the area. To the west (pictured at the bottom) in the image, the Glen Canyon Dam is barely visible. Built between 1960 and 1963, the dam provides the area with water, electricity, and recreation. However, the introduction of the dam permanently changed the local ecosystem: Glen Canyon was flooded to create Lake Powell. This led to a controversy that is often cited as the beginning of the modern environmental movement in America.