The San Gabriel River is a mostly-urban waterway flowing southward through Los Angeles and Orange Counties, California, in the United States. It is the central of three major rivers draining the Greater Los Angeles area, the others being the Los Angeles River and Santa Ana River. The river's watershed stretches from the rugged San Gabriel Mountains to the heavily developed San Gabriel Valley and a significant part of the Los Angeles coastal plain, emptying into the Pacific Ocean between the cities of Long Beach and Seal Beach.
The San Gabriel once ran across a vast alluvial flood plain, its channels shifting with winter floods and forming extensive wetlands along its perennial course, a relatively scarce source of fresh water in this arid region. The Tongva and their ancestors inhabited the San Gabriel River basin for thousands of years at villages like Puvunga, relying on the abundant fish and game in riparian habitats. The river is named for the nearby Mission San Gabriel Arcángel, established in 1771 during the Spanish colonization of California. Its water was heavily used for irrigation and ranching by Spanish, Mexican, and American settlers before urbanization began in the early 1900s, eventually transforming much of the watershed into industrial and suburban areas of greater Los Angeles.
Severe floods in 1914, 1934, and 1938 spurred Los Angeles County, and later the federal government, to build a system of dams and debris basins and to channelize much of the lower San Gabriel River with riprap or concrete banks. There is also an extensive system of spreading grounds and other works to capture stormwater runoff and conserve it for urban use. Approximately one-third of the water used in southeast Los Angeles County today comes from the river.
The upper San Gabriel has been intermittently mined for gold since the 1860s, and its deep gravel bed has been an important source of construction aggregate since the early 1900s. The river is also a popular recreation area, with parks and trails in the many flood basins along its course. The headwaters of the San Gabriel River have retained their natural character and are a popular attraction of the Angeles National Forest.
Geography and characteristics
The San Gabriel River basin drains a total of and is located between the watersheds of the Los Angeles River to the west, the Santa Ana River to the east, and the Mojave Desert to the north. The watershed is divided into three distinct sections. The northern third, located within the Angeles National Forest of the San Gabriel Mountains, is steep and mountainous; it receives the most precipitation of any part of the basin – per year – and as a result is the source of nearly all the natural runoff. Elevations reach up to at Mount San Antonio (Mount Baldy), the highest point of the range. During the winter, many elevations above are covered in snow.
The middle third, the San Gabriel Valley, and the southern third, the coastal plain of the Los Angeles Basin, are separated by the Puente Hills and Montebello Hills. With the exception of some recreation areas and lands set aside for flood control, the valleys are almost entirely urbanized. Approximately 2 million people live in the watershed, divided among 35 incorporated cities. Rainfall is slightly higher in the San Gabriel Valley than the coastal plain due to its proximity to the mountains; however, the climate as a whole is very arid, with only moderate precipitation in winter and nearly none in summer. The lower watershed consists primarily of alluvial plains that once experienced seasonal flooding from the San Gabriel River, creating vast swamps and wetlands. Today, very little of this original environment remains.
The San Gabriel is one of the largest natural streams in Southern California, but its discharge varies widely from year to year. Between 1895 and 1957 the mean unimpaired runoff at Azusa was estimated at , with a range from . Historically, the San Gabriel River reached its highest flows in the winter and spring, with runoff dropping significantly after early June before rising again with November or December storms. Today, the flow of the San Gabriel River has been dried up in places by dams, diversions, and groundwater recharge operations, and increased in other sections by wastewater run-off.
Headwaters East Fork The East Fork, long, is the largest headwater of the San Gabriel River; the U.S. Geological Survey considers it part of the main stem. However, it is colloquially known as the "East Fork" to distinguish it from the West Fork of the San Gabriel. Its furthest tributary, the Prairie Fork, originates at Pine Mountain in the Sheep Mountain Wilderness to the southwest of Wrightwood. Draining a high, remote, subalpine valley characterized by extensive meadows, it flows west to join with Vincent Gulch, below which the stream is officially known as the East Fork. Here it turns abruptly south, flowing through a steep, rugged canyon. It is joined from the east by the Fish Fork, which originates on the northwest slopes of Mount Baldy.
Below the Fish Fork, the East Fork flows through "the Narrows", one of the deepest gorges in Southern California. From the floor of the canyon at , Iron Mountain rises to the southeast, while Mount Hawkins, , rises to the northwest. The Iron Fork tributary joins from the west roughly in the middle of the Narrows. Near the lower end of the Narrows, the river passes under the Bridge to Nowhere, a arch bridge that was abandoned after the huge flood of 1938 washed out a highway under construction along the East Fork. The bridge remains today as a popular destination for hikers and bungee jumpers.
After emerging from the Narrows, the river continues flowing south through a somewhat-more-open valley, receiving several tributaries including Devil Gulch and Allison Gulch, before reaching Heaton Flat, a popular trailhead and the end of the East Fork Road, which parallels the lower section of the river. The river receives Cattle Canyon, its biggest tributary, and then turns sharply west, flowing past the Camp Williams Resort and a number of U.S. Forest Service and Los Angeles County firefighting facilities before flowing into San Gabriel Reservoir, where it joins the West Fork.
West Fork The West Fork, long, originates at Red Box Saddle, a visitor center and frequently used trailhead along the Angeles Crest Highway and about northwest of the summit of Mount Wilson. Beginning at an elevation of , the West Fork flows at a much lower elevation than the East Fork and is the smaller of the two rivers in terms of water volume. The West Fork flows east in a fairly straight course for its entire length. From its headwater, the river quickly descends to the Cogswell Reservoir, where Devils Canyon Creek joins from the north. The Gabrielino Trail parallels the river from Red Box Saddle as far as the Devore campground, above Cogswell Reservoir.
Below Cogswell Dam, the river is paralleled by Forest Route 2N25, a one-lane paved road open only to non-motorized traffic (except for maintenance and emergency services). The river flows east through a twisting canyon, forming the southern boundary of the San Gabriel Wilderness. It receives the tributaries of Chileno Canyon, Little Mermaids Canyon, and Big Mermaids Canyon from the north, and then the much larger Bear Creek, which originates at Islip Saddle near the summit of Mount Islip. Less than a mile (1.6 km) below Bear Creek, it is joined by the North Fork before flowing into San Gabriel Reservoir, where it joins with the East Fork.
North Fork The North Fork is the shortest and steepest of the three major forks. It begins as a series of streams falling off the crest of the range between Mount Islip and Mount Hawkins, more than above sea level. Cedar Creek flows south from Windy Gap, , to join with Soldier Creek, which continues south past Falling Springs to join with Coldbrook Creek, forming the North Fork. The North Fork continues south for past Valley of the Moon Plantation, forming a braided channel along its relatively wide canyon floor. It flows into the West Fork just below Hoot Owl Flats, a short distance from the larger river's mouth at San Gabriel Reservoir.
The North Fork is the most heavily developed fork of the San Gabriel River, with many campgrounds and facilities along its course. The popular Crystal Lake Recreation Area in the upper North Fork includes the only natural lake in the San Gabriel Mountains. The North Fork valley provides the route for Highway 39, which until 1978 provided automobile access from San Gabriel Canyon Road to the Angeles Crest Highway. Since then, the upper part of the road north of Crystal Lake has been closed due to chronic landslides and erosion. As of 2016, there are no plans to reopen the road.
San Gabriel Canyon
Below the confluence of the East Fork and West Fork, the San Gabriel River flows through the deep San Gabriel Canyon, the only major break in the southern part of the San Gabriel Mountains. Although this stretch of the river was once free-flowing, today is it impounded by major reservoirs for water supply and flood control. San Gabriel Dam, a high rockfill dam, forms the San Gabriel Reservoir. The concrete gravity Morris Dam, just downstream, creates the Morris Reservoir. A small hydroelectric plant in the city of Azusa is supplied with water from a diversion of the San Gabriel River, located directly below San Gabriel Dam.
The reservoir water levels fluctuate widely at the upper San Gabriel Reservoir, which serves mainly for flood control and sediment control. During the dry season the reservoir is often kept at a low level, in order to provide room for stormwater and allow county workers to remove built-up sediment from the basin. The northern part of the reservoir, when dry, is also used as the San Gabriel Canyon OHV area. There is no public boating access to either San Gabriel Reservoir or the downstream Morris Reservoir, which is used mainly for water supply. From World War II until the 1990s, Morris Reservoir was used by the U.S. Navy as a torpedo test site; the concrete launch ramp remains today and is easily seen from Highway 39, which runs through the canyon.
San Gabriel Valley The river emerges from the San Gabriel Canyon at Azusa, a short distance below Morris Dam, where it reaches the wide and gently sloping alluvial plain of the San Gabriel Valley. At the mouth of the canyon, the entire flow of the river, except during wet seasons, is diverted into the first of several spreading grounds that recharge the local San Gabriel Valley aquifer, an important source of local water supply. The usually-dry riverbed then continues in a southwesterly direction, passing the ruins of the 1907 Puente Largo or "Great Bridge" that once carried Pacific Electric interurban trains, and under Interstate 210 into the flood control basin behind Santa Fe Dam. There are 17 drop structures or grade controls along this roughly stretch of river bed, to prevent erosion down the valley's relatively steep slope.
Past the Santa Fe Dam – which when dry is used as the Santa Fe Dam Recreation Area – the river flows through Irwindale, where it is the site of several major gravel quarries, which have operated in the San Gabriel Valley since the early 1900s to mine the rich alluvial sediments deposited by the river over millennia. From here Interstate 605, the San Gabriel River Freeway, parallels the river's east bank almost all the way to its mouth in Seal Beach. Throughout the San Gabriel Valley, the river flows mainly in an earth-bottomed channel between artificial concrete or riprap banks. Shortly below Interstate 10 at El Monte, the river is joined from the east by Walnut Creek, which restores a small perennial flow. Below this confluence it curves west and receives San Jose Creek, also from the east, before passing under SR 60.