The San Pedro Valley is the western part of Cochise County Arizona, is a 50-mile-long (80 km), mostly north–south valley, trending northwesterly. The San Pedro River drains from the state of Sonora, Mexico, through Benson, Arizona, and the southeast of the Rincon Mountains.
The San Pedro Valley is a site for Holocene mammal fossils because of the riparian environment. In recent decades, the Arizona Geological Society has focused on the region, as well as researchers. Development pressures, recreation, and groundwater harvesting have led to recent concerns of protecting the region. A recent floodplain study focused on the Holocene floodplain alluvium and its history, over a 125-mile (201 km) stretch of the river to understand subground waterflow resources.
Since the 1870s, the San Pedro valley has been home to small communities engaged in cattle ranching, mining, agriculture, and more recently, tourism. The valley bottomland changed dramatically as modification to the San Pedro River corridor – draining cienegas, constructing irrigation ditches, and building railroads and roads – modified the river floodplain, altered the riparian and valley ecology, and transformed the San Pedro River from a low-energy, broadly meandering stream into a higher energy, entrenched watercourse with a deeply incised channel. Natural factors may have also contributed to entrenchment. The San Pedro Valley in surrounded by the Huachuca, Mule, Whetstone, Dragoon, Rincon, Winchester, Galiuro, Santa Catalina and Tortilla Mountains.