The Nature Conservancy. Protecting nature. Preserving life.™

Aerial view of the San Pedro River, Mexico © Adriel Heisley

The 55-million-acre Sonoran desert stretches across Mexico and the United States, including the Mexican states of Sonora and Baja California and southern parts of the U.S. states of Arizona, California and New Mexico.

Its beauty is in its expansive, colorful vistas of saguaro cactus, grasslands, mountains and the life-sustaining waterways that flow through this desert landscape. Ranching defines the culture of the people who live here in both Mexico and the U.S. 

The myriad habitats that form the desert make it a haven for wildlife, teeming with Sonoran pronghorn and bighorn sheep. Peregrine falcons and golden and bald eagles soar overhead, and the Mexican spotted owls can be seen.

Black bear and Mexican gray wolf are found in the desert and, occasionally, the distant roar of a jaguar or mountain lion can be heard. The black-tailed prairie dog also calls the Sonoran Desert home.

Grasslands and river beds

The San Pedro River emerges from the western Sierra Madre Mountains creating a ribbon of life as it flows from the forested highlands through the lowland grassland prairies. The river basin is a critical site for more than 400 species of migratory birds and a wildlife corridor for 80 species of mammals.

The extensive grasslands surrounding the San Pedro River are some of the best preserved in the region and harbor the black-tailed prairie dog and Mexican gray wolf. Unique freshwater pools known as ciénegas occur within these grassland prairies and support native fish and amphibian species including the Gila chub and Huachuca tiger salamander.

The biological diversity of the Sonoran Desert and grasslands is threatened by the introduction of invasive species, cattle ranching, agriculture, road and infrastructure development, groundwater depletion, mining, sand and rock extraction, catastrophic fires, logging, illegal hunting and destructive recreational activities.

Revitalizing the San Pedro River Basin

Conservationists on both sides of the U.S.-Mexico border have been working with private landowners to revitalize the San Pedro River, its tributaries and watersheds.

In Jaunary 2005 the Conservancy and its local partners Biodiversidad y Desarrollo Armónico (BIDA) and Naturalia purchased the 10,000-acre Rancho Los Fresnos property containing high quality grasslands and ecologically important ciénegas. A research station was established on the site and prescribed burns are being implemented to reintroduce a natural fire regime in the region’s grasslands. 

The ranch is now a regional demonstration site for conservation and restoration of grasslands, wetlands and critical freshwater habitats.