Sonora, Mexico

San Pedro River (Mexico)

The San Pedro River is a north flowing river with its headwaters in the northern Mexico state of Sonora. It flows 140 miles north to its junction with the Gila River in south central Arizona. The San Pedro is one of the last rivers in the west that has escaped being dammed. Extended lengths of the northern region of the river remain dry most of the year, relying heavily on the monsoon rains to generate water flow. The headwaters of the San Pedro River originate from the high slopes of the Sierra La Mariquita, Sierra San Jose, and Sierra Los Ajos mountains in north central Sonora, Mexico. Flowing northward, the San Pedro River passes through the rolling semi-arid grasslands of the Chihuahuan Desert and Sonoran Desert into Arizona, where it enters a broad valley flanked by mountains on the east and west. The western mountain ranges within the United States include the Huachuca Mountains, the Whetstone Mountains and the Rincon Mountains. The eastern mountain ranges include the Mule Mountains, the Dragoon Mountains and the Galiuro Mountains.


This river is a very important riparian area for hundreds of species of plants, mammals, reptiles and insects, and is a major bird migratory path as well. More than 300 species of birds, 200 species of butterflies and 20 species of bats use this corridor as they migrate between South, Central and North America.


Humans have populated the San Pedro River valley since the earliest times. Several very significant Paleo Indian sites have been discovered along the San Pedro, in which spear points have been found in the remains of mammoths and other large mammals of the Ice age era, dating back 12,000 years. Other native American tribes, primarily of the Hohokam culture, have populated the area later in history as well. The first European to discover the river was Francisco Vasquez de Coronado in 1540, in search of the legendary Seven Cities of Cibola, cities reportedly made of gold.

In recent decades, rapid growth and population increases in southern Arizona has caused concern with this river, and whether or not it can survive the extensive ground water pumping that now occurs in the area. Several non-profit organizations have risen in recent years to address awareness to this problem.

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