6.6 SAN JUAN BASIN
The San Juan Basin is a Laramide-age (late Cretaceous-early Tertiary) asymmetric structural basin that encompasses a surface area of approximately 21,600 square miles in Colorado, New Mexico, Utah, and Arizona. The basin occupies the eastern third of the Colorado Plateau physiographic province and is characterized by rugged terrain. Landscape features include mesas, terraces, escarpments, canyons, dry washes (arroyos), and mountains.
The Hogback Monocline along the northern portion of the San Juan Basin.
Cretaceous age rock units dip south (left) towards the center of the basin.
Photo by L. Scott, CGS.
Several major rivers, including the San Juan, Los Pinos, Florida, Animas, and La Plata, flow through Colorado’s portion of the San Juan Basin. All of the rivers flow southward into New Mexico and are part of the Colorado River system via the San Juan River. The entirety of the Colorado portion of the basin is included in Water Division 7 (Figure 6.6-1).
In Colorado, the San Juan Basin extends into Archuleta, La Plata, and Montezuma counties. Much of the land located in the Colorado portion of the basin belongs to the Southern Ute Indian Reservation. Land use in southwestern Colorado is highly variable including irrigated-agriculture, ranches and residential lots clustered around the main community centers. The San Juan Basin is a significant producer of coal, oil, and natural gas. As of February 2001, almost 5,000 permitted water wells of record are present in the Colorado portion of the San Juan Basin, as depicted in Figure 6.6-1.