The San Pedro drains an area of approximately 4,720 square miles (12,200 km²) in Cochise, Graham, Pima, and Pinal Counties.
Its course traverses deep sedimentary basins flanked by the Huachuca, Mule, Whetstone, Dragoon, Rincon, Little Rincon, Winchester, Galiuro, Tortilla, and Santa Catalina Mountains.
The San Pedro is fed by numerous tributaries, which in general, drain relatively short and steep catchments oriented more or less perpendicular to the mainstem.
For most of its length the San Pedro flows over sedimentary basin fill deposits, although it is bound by bedrock at the Tombstone Hills at Charleston and near Fairbank, “the Narrows” south of Cascabel, near Redington, and again at Dudleyville (Heindl, 1952).
Two major tributaries, Babocomari River and Aravaipa Creek, each have extensive bedrock-lined stretches.
Historically the San Pedro has been divided into upper and lower reaches at the Narrows.

On May 27, 2011, a U.S. District judge ruled that Fort Huachaca's plan to pump 6,100 acre feet (7,500,000 m³) of groundwater without mitigation plans to replenish the San Pedro River flows failed to protect the endangered Southwestern willow flycatcher (Empidonax traillii) and the Huachuca water umbel so they could recover from their imperiled status.
The ruling was in response to a second lawsuit brought by the Center for Biological Diversity and the Maricopa Audubon Society.
In 2002, in response to an earlier suit filed by the center, another judge tossed out an earlier Wildlife Service biological opinion that the water pumping could be mitigated.
The San Pedro drains an area of approximately 4,720 square miles (12,200 km²) in Cochise, Graham, Pima, and Pinal Counties. Its course traverses deep sedimentary basins flanked by the Huachuca, Mule, Whetstone, Dragoon, Rincon, Little Rincon, Winchester, Galiuro, Tortilla, and Santa Catalina Mountains. The San Pedro is fed by numerous tributaries, which in general, drain relatively short and steep catchments oriented more or less perpendicular to the mainstem. For most of its length the San Pedro flows over sedimentary basin fill deposits, although it is bound by bedrock at the Tombstone Hills at Charleston and near Fairbank, “the Narrows” south of Cascabel, near Redington, and again at Dudleyville (Heindl, 1952). Two major tributaries, Babocomari River and Aravaipa Creek, each have extensive bedrock-lined stretches. Historically the San Pedro has been divided into upper and lower reaches at the Narrows.
On May 27, 2011, a U.S. District judge ruled that Fort Huachaca's plan to pump 6,100 acre feet (7,500,000 m³) of groundwater without mitigation plans to replenish the San Pedro River flows failed to protect the endangered Southwestern willow flycatcher (Empidonax traillii) and the Huachuca water umbel so they could recover from their imperiled status. The ruling was in response to a second lawsuit brought by the Center for Biological Diversity and the Maricopa Audubon Society. In 2002, in response to an earlier suit filed by the center, another judge tossed out an earlier Wildlife Service biological opinion that the water pumping could be mitigated.
San Pedro River (Arizona)