Gila River 2020


Frequently referred to as the cornerstone of southern New Mexico, the Gila River remains the state’s last free-flowing river and one of the longest rivers in the western United States. Despite the many ongoing threats, this iconic natural feature of the American Southwest is very rich in biodiversity. The area where the three forks of the Gila River converge is known as the Gila Wilderness and is considered the First federally designated wilderness area in the United States.

Course of the Gila River

Three hikers hike through the Middle Fork Gila River in Gila National Forest, New Mexico.

The Gila River, which spans the two US states of New Mexico and Arizona, flows over 600 miles. As a tributary of the Colorado River, the Gila River is fed by six major tributaries. The three main forks of the river, which are the West Fork, the Middle Fork, and the East Fork, are in the Black Range on the Continental Divide. After originating in Sierra County in western New Mexico, the Gila River flows along the Mogollon Mountains and southwest into the Gila National Forest and the Gila Cliff Dwellings National Monument. In turn, the river passes the town of Safford in western Arizona before converging with the Colorado River in southwestern Arizona. Although it is considered one of the longest rivers in the western United States, the many irrigation diversions of the Gila River dry it up before it reaches the first 500 miles of its journey. So what could once be traversed by large river boats has been reduced to a mere intermittent trickle by the time it reaches the Gila River Indian Reservation. Additionally, the Gila River drains a watershed of approximately 60,000 square miles. Although primarily in the United States, the watershed extends into the northern Sonora region of Mexico. This watershed is so large that it covers an area larger than the entire Green River basin. To add, it is four times larger than Idaho’s Salmon River drainage.

The climate of the Gila River

The spring season sees the snow melting on the Sky Islands and the Mogollon Rim Mountains. This leads to the gradual and predictable flow of the Gila River and its tributaries. In early summer, the vast majority, if not all, of the snow on these mountains melts. The flow of the river is greatly reduced to a simple trickle, especially towards the end of its course. Nevertheless, the dry river is replenished with the arrival of the southern monsoons around mid to late summer. This is further enhanced by the periodic frontal storms in the fall and winter seasons. Additionally, these rainfall events can cause flooding, as massive amounts of water are released into the river system in a short period of time.

Brief History of the Gila River

Gila River in the Gila Cliff Dwellings National Monument, New Mexico
Gila River in the Gila Cliff Dwellings National Monument, New Mexico.

The Gila River has been exposed to many agricultural and human activities throughout history. For example, the indigenous Hohokam people managed to build complex civilizations along the banks of the Middle Gila River. This was achieved by creating hundreds of kilometers of irrigation canals which drew their water from the Gila River itself. The river was later discovered and visited by several European explorers. The river actually marked the southern border of the United States between 1848 and 1853. In the 19th century, European settlers began to restructure the course and flow of the river. This was achieved by constructing diversions and small-scale dams to protect crops from seasonal floods and droughts. The valley saw a substantial increase in population after 1928, when the federal government completed the Coolidge Dam on the Gila River itself. Growing agricultural demand has led farmers to dramatically increase groundwater pumping methods. Despite this, the continued demand for water led to the creation of the Central Arizona Project (CAP), a $4 billion aqueduct project to transport billions of gallons of water from the Colorado River. The PAC has been successful in meeting the water and agricultural needs of large cities like Tucson and Phoenix. However, these monumental gains for the human population have been achieved by jeopardizing much of the ecosystems of the Gila River and its tributaries. Nonetheless, the area continues to be a critical region for wildlife, particularly after Aldo Leopold convinced the US Forest Service in 1924 to establish the area as the first wilderness area designated by the United States Congress.

Gila River Ecology

A massive American bullfrog in the Gila National Forest
A huge American Bullfrog sits in the mud next to the Middle Fork Gila River, Gila National Forest, New Mexico.

The Gila River flows through several iconic ecosystems, such as the huge poplar and willow forests as well as the arid Sonoran Desert. Thus, the waters of the river provide vital habitats for a wide variety of organisms, many of which are found nowhere else. This includes over 300 species of migratory bird species, as well as several that are endemic to the region. Among these bird species found only in the Gila Wilderness are the Bearded Tyrannulet and the Common Blackhawk. Other bird species that inhabit this high-quality habitat include the Southwestern Willow Flycatcher, Montezuma Quail, Elven Owl, and the endangered Yellow-billed Cuckoo. Given the river’s highly varied landscape, with ponderosa pine forests, the area is home to cougars, bighorn sheep, pronghorn, elk, and black bears. Additionally, the area is also home to the world’s largest population of rare Mexican spotted owls as well as several populations of reintroduced endangered Mexican wolves. Another endangered species that inhabits the ecosystems of the river is the Mexican garter snake. The river also contains high levels of aquatic diversity, especially as many native fish species have become highly adapted to the region’s heavy seasonal rainfall. For example, the Gila topminnow has evolved several behavioral adaptations that allow it to avoid being swept downstream during floods. In contrast, the high elevation portions of the watershed tend to contain the most fish populations. Thus, it is in these portions that the endangered Gila trout are most often found.


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