This area is part of the basin and range geologic region, characterized by linear mountain ranges which are separated by broad, flat basins. The region was impacted by relatively recent volcanic activity, leaving volcanic plugs and cinder cones visible throughout the San Bernardino Valley. Earthquakes have further altered the region and helped allow the flow of many springs and seeps. All of these dynamic geological events have played major roles in shaping the valley, catching and storing crucial water, helping determine the variety of plants and animals present, and creating a beautiful landscape for humans to enjoy.

The San Bernardino Valley once supported permanently flowing creeks, springs, and marshy wetlands. In addition, the giant sacaton grassland in the valley was once described as "a luxuriant meadow some eight or ten miles long and a mile wide." The dependable source of water and grass made the area not only invaluable to a huge diversity of fish and wildlife, but also a center of human activity for centuries.

With expanding settlement beginning in the late 1800's came farming, mining, and livestock production, all of which competed for the same precious water. While the extensive wetlands here once provided historic habitat for eight different kinds of native fish, the lowering water table led to severe changes in the habitat and the eventual local extinctions of many species.

Protection and restoration of the region's springs, ponds, and streams in both the United States and in Mexico by private landowners, conservation organizations, and government agencies will help ensure that the delicate ecological balance that has been in place for centuries will continue to provide quality habitat for all fish, wildlife, and humans dependent upon the Rió Yaqui Basin.

Fish recovery actions include stabilization of existing populations, establishment of self-sustaining populations, and extensive restoration of wetland habitat. Many ongoing management actions are occurring on the refuges and on adjacent private lands. Eroded stream channels are being restored through the placement of rock-filled, wire-basket gabions and through cottonwood and willow plantings. Old agricultural fields are being reclaimed to recreate valuable ciénega wetland conditions. Damaged uplands are being re-vegetated with native grasses. Invasive, non-native species are being removed or controlled. Slowly, the land and its associated fish and wildlife is recovering.

Historically, fire was a part of this ecosystem and was crucial to maintaining healthy habitats. However, humans settling this land initially tended to favor fire suppression, therefore preventing periodic natural fires from removing decadent vegetation and recycling important nutrients. As a result, plant species such as mesquite, with its deep root structure, were able to gain an advantage and out-complete most other native plants.

Fire is an effective tool in habitat recovery actions. Controlled fire is now being introduced back into the system to help rejuvenate native grasses and help control the spread of mesquite trees.