The San Bernardino Refuge lies at the headwaters of the Río Yaqui, a large river that drains portions of southeastern Arizona and southwestern New Mexico in the United States, as well as eastern Sonora and western Chihuahua in Mexico.  Within this basin, the San Bernardino ciénega (a marshy wetland) has historically been considered the largest, most extensive wetland in northwest Mexico and this region of the Southwest.  It provides an important link for wildlife to migrate between Mexico’s Sierra Madre Occidental and the Rocky Mountains to the north.

The refuge’s surrounding landscape is characterized by linear mountain ranges separated by broad, flat basins.  On a geologic time frame, the San Bernardino Valley was recently impacted by volcanic activity and as a result, many volcanic plugs and cinder cones are visible throughout the region.  Earthquakes, some as recent as the late 1800’s, altered the valley’s landscape.  Many springs began to flow and seeps emerged.  All of these geological events shaped the valley, catching and storing crucial water and helping determine the variety of plants and animals present.

Between the San Bernardino and nearby Leslie Canyon Refuge, at least 335 bird species have been recorded, including many nesting birds.  In addition, 67 mammal, 43 reptile, 13 amphibian, and eight fish species have been documented.  The two refuges are critical in maintaining a sanctuary for at least 36 plant and wildlife species of special concern. 

In addition to the diversity of birds, mammals, amphibians and reptiles, this region is also known for having the highest diversity of bees in the world with approximately 500 different species collected.  Where the San Bernardino Refuge is located, the San Bernardino Valley, is an amazing diversity of pollinators in general, including the black-chinned hummingbird, broad-billed hummingbird, lesser long-nosed bat and more than seventy-five species of butterflies.