The Little Colorado River () is a tributary of the Colorado River in the U.S. state of Arizona, providing the principal drainage from the Painted Desert region. Together with its major tributary, the Puerco River, it drains an area of about in eastern Arizona and western New Mexico. Although it stretches almost , only the headwaters and the lowermost reaches flow year-round. Between St. Johns and Cameron, most of the river is a wide, braided wash, only containing water after heavy snowmelt or flash flooding.
The lower is known as the Little Colorado River Gorge and forms one of the largest arms of the Grand Canyon, at over deep where it joins the Colorado near Desert View in Grand Canyon National Park. An overlook of the gorge is a Navajo Nation Tribal Park.
Course
The river rises as two forks in the White Mountains of mid-eastern Arizona, in Apache County. The West Fork starts in a valley on the north flank of Mount Baldy at an elevation of nearly , while the East Fork starts nearby. The forks meet in a canyon near the town of Greer, forming the main Little Colorado River. It flows into River Reservoir, then leaves the canyon near Eagar. The river then turns north, meandering through Richville Valley, before emptying into Lyman Lake, impounded by an irrigation dam built in 1912. From there the river continues north, past the town of St. Johns. Shortly afterwards, the river transforms from a perennial stream to an ephemeral wash as it travels northwestwards through Hunt Valley, where it receives the Zuni River, then receiving Silver Creek and the Puerco River—its main tributaries—near the town of Holbrook as it flows into the Painted Desert.
The Little Colorado passes Joseph City and crosses the Southern Transcon route of the BNSF Railway (originally the Atchison, Topeka and Santa Fe Railroad), now winding north into Coconino County. The river enters the Navajo Nation, and drops over the Grand Falls of the Little Colorado shortly after. Below Grand Falls, the river flows through a short but rugged canyon for about . Emerging into the desert again, the Little Colorado skirts the eastern edge of Wupatki National Monument and passes the town of Cameron, where it is bridged by U.S. Highway 89.
From Cameron, the Little Colorado River carves an extremely steep and narrow gorge into the Colorado Plateau, eventually achieving a maximum depth of about . The depth of the canyon is such that groundwater is forced to the surface, forming numerous springs that restore a perennial river flow. It joins the Colorado deep inside the Grand Canyon, miles from any major settlement. The confluence marks the end of the Marble Canyon segment of the Grand Canyon and the beginning of Upper Granite Gorge.
Discharge
The Little Colorado River is one of the two major tributaries of the Colorado River in Arizona, the other being the Gila River. Runoff typically peaks twice a year, first in the early spring (February–April) from snow melt and highland rain; and in the summer (July–September) from monsoon storms. The annual runoff is extremely variable with the possibility of no flow occurring due to a weak snow pack or lack of summer rain. Conversely, years such as 1949, 1973, 1979, 1983 and 1993 have seen massive volumes of spring snowmelt while large monsoon runoff has occurred in 1955, 1964, 1984 and 2006. Monthly average flows in the springtime average several hundred cfs and can reach . Only the upper reaches of the river above St. Johns, and the lowermost stretch below Cameron, flow year round; the middle section is basically a huge arroyo that carries water only during the wet seasons.
According to a streamflow gauge near Cameron, before the river enters the Grand Canyon, the river's average annual flow was from 1948 to present. The highest annual average was in 1973, and the lowest was in 2000. The river's peak flows can be far higher than its average flow, because of quick desert runoff from cloudbursts. At the same gauge, peak flows were recorded from 1923 to 2008, with spotty data from 1924 to 1947. The highest recorded peak was on September 20, 1923, while the lowest was in 1974.
History
Human activity in the Little Colorado River watershed dates back to the early Holocene epoch, in the last glacial period. Nomadic hunter-gatherers inhabited the relatively water-rich and diverse upper basin of the Little Colorado for almost 8,000 years before the Navajo, Apache and Hopi tribes populated the area. Many of these people practiced small-scale irrigation in riverside villages, located in sheltered canyons and cliffs that provided defense.