The primary purpose for the designation is to protect and enhance the desert riparian ecosystem, a rare remnant of what was once an extensive network of similar riparian systems throughout the Southwest. The word riparian refers to an area where plants and animals thrive because of an availability of water, either at or near the soil surface. The San Pedro River enters Arizona from Sonora, Mexico, flows north between the Huachuca and Mule mountains ranges, and joins the Gila River 100 miles downstream near the town of Winkelman. The San Pedro's perennial flow, though sometimes a trickle, is a rare occurrence in the Southwest.
Water is the critical element in a riparian ecosystem.
Without an adequate, continuous supply, the ecosystem would surely perish. The San Pedro Riparian National Conservation Area, known for its extensive riparian corridor, is a composite of several vegetation communities. Fremont cottonwood and Goodding willow dominate the riparian corridor. Lesser amounts of Arizona ash and walnut, netleaf hackberry, and soapberry occur as well. Chihuahuan desert-scrub, typified by thorny species such as tarbush, creosote and acacia, characterize the uplands bordering both sides of the river, while mesquite and sacaton grass dominate the bottomland adjacent to the riparian corridor.