The Rio San Bernardino, or San Bernardino River, begins in extreme southeastern Cochise County, Arizona

Cochise County, Arizona

-2010:Whereas according to the 2010 U.S. Census Bureau:*78.5% White*4.2% Black*1.2% Native American*1.9% Asian*0.3% Native Hawaiian or Pacific Islander*4.0% Two or more races*9.6% Other races*32.4% Hispanic or Latino -2000:...

 and is a tributary of the Bavispe River

Bavispe River

The Rio Bavispe or Bavispe River is a river in Mexico which flows briefly north then mainly south by southwest until it joins with the Aros River to become the Yaqui River, eventually joining the Gulf of California.-History:...

, in Sonora

Sonora

Sonora officially Estado Libre y Soberano de Sonora is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided into 72 municipalities; the capital city is Hermosillo....

, Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

. It is named after one of Southern California

Southern California

Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...

's largest cities, San Bernardino

San Bernardino

San Bernardino, California is a large city in the Inland Empire Metropolitan Area of Southern California.San Bernardino may also refer to:-Landforms:*San Bernardino , a torrent that flows through the Italian province of Verbano-Cusio-Ossola...

.

Watershed

The Rio San Bernardino has two major tributaries, the Rio Agua Prieta and the Cajón Bonito. The river's headwaters are in extreme southeastern Cochise County, Arizona as Black Draw. From here the Rio San Bernardino flows south, crossing into Mexico east of Douglas, Arizona

Douglas, Arizona

Douglas is a city in Cochise County, Arizona, United States. Douglas has a border crossing with Mexico and a history of mining.The population was 14,312 at the 2000 census...

. In northern Sonora

Sonora

Sonora officially Estado Libre y Soberano de Sonora is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided into 72 municipalities; the capital city is Hermosillo....

, the Cajón Bonito River joins the San Bernardino River in the San Bernardino Valley

San Bernardino Valley (Arizona)

The San Bernardino Valley of Arizona is a northeast by southwest trending valley in extreme southeast Cochise County, Arizona.The north end of the valley merges into the northwest by southeast trending San Simon Valley; both merge in western Hidaldgo County, New Mexico...

 after draining the Sierra San Luis

Sierra San Luis

The Sierra San Luis range is a mountain range in northwest Chihuahua, northeast Sonora, Mexico at the northern region of the Sierra Madre Occidental cordillera...

 and northern end of the Sierra Madre Occidental

Sierra Madre Occidental

The Sierra Madre Occidental is a mountain range in western Mexico.-Setting:The range runs north to south, from just south of the Sonora–Arizona border southeast through eastern Sonora, western Chihuahua, Sinaloa, Durango, Zacatecas, Nayarit, Jalisco, Aguascalientes to Guanajuato, where it joins...

. Next the Rio San Bernardino is joined by the Rio Agua Prieta which also begins in Cochise County, crossing south from Black Draw into Mexico at Agua Prieta

Agua Prieta

Agua Prieta is a pueblo and municipality in the northeastern corner of the Mexican state of Sonora . It stands on the U.S.–Mexico border, adjacent to the town of Douglas, Arizona, USA. The municipality covers an area of 3,631.65 km²...

 and Douglas

Douglas, Arizona

Douglas is a city in Cochise County, Arizona, United States. Douglas has a border crossing with Mexico and a history of mining.The population was 14,312 at the 2000 census...

. The Rio Agua Prieta flows south and east to join the Rio San Bernardino, shortly after the Rio Agua Prieta meets up with the Rio Fronteras, the latter flowing north from near Nacozari de Garcia, Sonora. The San Bernardino River joins the Bavispe River

Bavispe River

The Rio Bavispe or Bavispe River is a river in Mexico which flows briefly north then mainly south by southwest until it joins with the Aros River to become the Yaqui River, eventually joining the Gulf of California.-History:...

 at Morelos, Sonora at the northern end of the Sierra del Tigre

Sierra del Tigre

Sierra del Tigre is a mountain range in northeastern Sonora, Mexico at the northern region of the Sierra Madre Occidental. The region contains sky island mountain ranges, called the Madrean Sky Islands, some separated from the Sierra Madre Occidental proper, and occurring in the northeastern...

. The Bavispe River flows south by southwest to the Yaqui River

Yaqui River

The Yaqui River is a river in the state of Sonora in northwestern Mexico. Being the largest river system in the state of Sonora, the Yaqui river is used for irrigation....

 and eventually to the Gulf of California

Gulf of California

The Gulf of California is a body of water that separates the Baja California Peninsula from the Mexican mainland...

 at Guaymas, Sonora.

Ecology

North American beaver (Castor canadensis) were documented by Leopold in 1977 in northern Mexico, and a 2000 survey found five breeding pairs of beavers on the Cajón Bonito River mostly in remote ranches without livestock. The authors of the latter study reported that local ranchers kill beavers because they fear felled trees will block roads. However, beavers are considered keystone species and ecosystem engineers, as their dams raise the water table and turn seasonal stretches of streams into perennial reaches, producing highly beneficial impacts on species abundance and diversity in the riparian zone. Beavers were also documented by Hendrickson et al in 1978 on the Cajón Bonito.