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91-647: The San Gabriel River is a mostly- urban waterway flowing 58 miles (93 km) 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

182-548: 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

273-643: A greater presence of urban stream syndrome. Hydrology plays a key role in urban stream syndrome. As urbanization of these streams continue, there is in turn a decrease in the perviousness of the catchment to precipitation, which leads to a decrease in the infiltration and an increase in the surface runoff . This can cause problems during flood discharges. For example, flood discharges in urban catchments were at least 250% higher in urban catchments than in forested catchments in New York and Texas during similar storms. Many water managers treat USS by directly addressing

364-488: 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

455-522: A nearly straight line from east to west across the center of the San Gabriel Mountains . In the winter, the mountain regions are prone to landslides and destructive debris flows , which has required the construction of many debris basins to protect foothill communities such as Glendora and Monrovia , but these works have not always been effective during the biggest storms. During floods, the river transports large volumes of sediment from

546-519: 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. The West Fork , 19 miles (31 km) long, originates at Red Box Saddle , a visitor center and frequently-used trailhead along the Angeles Crest Highway and about 2 miles (3.2 km) northwest of the summit of Mount Wilson . Beginning at an elevation of 4,666 feet (1,422 m),

637-610: A popular attraction of the Angeles National Forest . The San Gabriel River basin drains a total of 689 square miles (1,780 km) 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

728-499: A recreational fishery. About 60,000 rainbows are stocked each year between October and June. The West Fork also has the largest remaining population of arroyo chub , a fish endemic to coastal Southern California streams. Although the first recorded inhabitants of the San Gabriel River area arrived about 2,500 years ago, humans may have been present in Southern California as early as 12,000 years ago. Immediately prior to

819-458: A rich lowland ecosystem on its broad floodplain, inundated multiple times each year by rain and snowmelt. The result of this overflow was a 47,000-acre (19,000 ha) network of riparian and wetland habitats, ranging from seasonally-flooded areas in the north to alkali meadows (called "cienegas" by the Spanish), forests of willows, oaks, and cottonwoods, and both fresh- and salt-water marshes in

910-532: 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

1001-648: 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 3,000 feet (910 m), Iron Mountain rises 8,007 feet (2,441 m) to the southeast, while Mount Hawkins, 8,850 feet (2,700 m), rises to

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1092-669: A system of large land grants which became the many ranchos of the area. The decline of Native American populations made it easy for colonists to seize large areas of land formerly used by the indigenous people. During the Spanish-controlled period, and the Mexican-controlled period between 1821 and 1846, cattle ranching dominated the local economy. In the San Gabriel River watershed, the Rancho Azusa de Dalton and Rancho Azusa de Duarte lay, respectively, to

1183-410: Is Onondaga Lake . Historically one of the most polluted freshwater lakes in the world, its salinity and toxic constituents like mercury rose to unsafe levels as large corporations begun to set up shop around the lake. High levels of salinity would be disastrous for any native freshwater marine life and pollutants like mercury are dangerous to most organisms. Higher levels of urbanization typically mean

1274-402: Is commonly found in areas near or in urban areas. USS also considers hydrogeomorphology changes which are characterized by a deeper, wider catchment, reduced living space for biota, and altered sediment transport rates. Keep in mind the status of water quality is difficult to assess in urban areas because of the complexity of the pollutions sources. This could be from mining and deforestation, but

1365-555: 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 2-mile (3.2 km) stretch of river bed, to prevent erosion down

1456-491: Is loose clay , silt , sand , or gravel that has been deposited by running water in a stream bed, on a floodplain , in an alluvial fan or beach , or in similar settings. Alluvium is also sometimes called alluvial deposit . Alluvium is typically geologically young and is not consolidated into solid rock. Sediments deposited underwater, in seas, estuaries , lakes, or ponds, are not described as alluvium. Floodplain alluvium can be highly fertile, and supported some of

1547-515: 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 114,000 acre-feet (141,000,000 m), with a range from 9,600 to 410,000 acre-feet (11,800,000 to 505,700,000 m). 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,

1638-550: The Metro C Line , then crossing under SR 91 at Bellflower . The San Gabriel River Bike Trail parallels the river starting at Whittier Narrows for 28 miles (45 km) to the Pacific Ocean at Seal Beach. From Cerritos the river flows south-southeast until reaching its confluence with Coyote Creek , the largest tributary of the lower river, which drains much of northwest Orange County. A short distance below Coyote Creek,

1729-673: The San Andreas Fault (the boundary between the North American Plate and Pacific Plate ) and its subsidiary fault and fracture zones. The San Gabriel Mountains are a fault block mountain range, essentially a massive chunk of bedrock dislocated from the North American Plate and lifted up by movement along the San Andreas. The rock is mostly of Mesozoic origin (65–245 million years old), but

1820-416: 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. Below the confluence of the East Fork and West Fork,

1911-599: 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

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2002-601: The Santa Ana River . Once every few decades, a particularly intense storm would cause the rivers to burst their banks simultaneously, inundating the coastal plain in a continuous sheet of floodwater. The historical floodplain encompassed much of the San Gabriel Valley and a huge expanse of the Los Angeles Basin stretching from present-day Whittier to Seal Beach. The thick sediments of the lowland also trap an extensive local aquifer system. Historically,

2093-682: The West Fork of the San Gabriel. Its furthest tributary, the Prairie Fork, originates at 9,648-foot (2,941 m) 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

2184-487: The last ice age when the regional climate was much wetter. The montane forests are home to large mammals such as deer and black bears. Due to conservation policies put in place by the 19th century, the upper San Gabriel watershed was never subjected to heavy logging. Also in the San Gabriel River watershed is the 17,000-acre (6,900 ha) San Dimas Experimental Forest , a UNESCO Biosphere Reserve where forest hydrology has been continually studied since 1933. Lower down in

2275-645: The 19th century, the term had come to mean recent sediments deposited by rivers on top of older diluvium , which was similar in character but interpreted as sediments deposited by Noah's flood . With the rejection by geologists of the concept of a primordial universal flood, the term "diluvium" fell into disfavor and was replaced with "older alluvium". At the same time, the term "alluvium" came to mean all sediment deposits due to running water on plains. The definition gradually expanded to include deposits in estuaries, coasts, and young rock of marine and fluvial origin. Alluvium and diluvium were grouped as colluvium in

2366-412: The 27,800-acre-foot (34,300,000 m) 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

2457-560: 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

2548-569: The East Fork, grew to include "a boarding house, two or three stores, blacksmith shop, butcher shop, etc." A flood in November 1859 destroyed the settlement, but four months later it was re-established as the town of Eldoradoville , near the junction of the East Fork and Cattle Canyon. The period from 1859 to 1862 was the most prosperous of the San Gabriel gold rush; Wells Fargo stages alone shipped some $ 15,000 ($ 457,800 in 2023 dollars) worth of gold per month out of Los Angeles County, most of it from

2639-551: 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

2730-399: The Pacific Ocean to spawn, and it was known as one of the "best steelhead fishing rivers in the state". Irrigation development that dried up the river, and later damming and channelization for flood control, have contributed to the near extinction of steelhead in the San Gabriel basin. Since the 19th century rainbow trout have been planted in the upper forks of the San Gabriel River to provide

2821-542: The San Gabriel Canyon long before California became a U.S. state, gold was first confirmed in the upper San Gabriel River around April 1855, by a party of prospectors who had entered the mountains via Cajon Pass . The Los Angeles Star soon reported of their findings: There has been some excitement this past week about the new gold diggings on the headwaters of the San Gabriel. We have met several persons who have been prospecting and although they found gold of

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2912-514: The San Gabriel Mountains, is steep and mountainous; it receives the most precipitation of any part of the basin – 33 inches (840 mm) per year – and as a result is the source of nearly all the natural runoff. Elevations reach up to 10,064 feet (3,068 m) at Mount San Antonio (Mount Baldy), the highest point of the range. During the winter, many elevations above 6,000 feet (1,800 m) are covered in snow. The middle third,

3003-454: 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

3094-467: 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 325-foot (99 m) high rockfill dam, forms the 44,183-acre-foot (54,499,000 m) San Gabriel Reservoir . The concrete gravity Morris Dam , just downstream, creates

3185-438: 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

3276-403: The San Gabriel Valley, resulting in a severe decline of the water table as farmers drilled hundreds of wells. The San Gabriel Valley aquifer is now an important source of domestic and industrial water, and groundwater recharge operations are conducted using both local runoff from the San Gabriel River, and water imported through Los Angeles's aqueduct system. The San Gabriel River once supported

3367-652: The San Gabriel diggings. John Robb, who ran a saloon in Eldoradoville, claimed he "made more money by running the sawdust from the floor of the Union Saloon through his sluice box than he was able to make from real mining, so prodigal and careless of their pokes were the miners and gamblers of those days." Urban stream Governments may alter the flow or course of an urban stream to prevent localized flooding by river engineering : lining stream beds with concrete or other hardscape materials, diverting

3458-473: The San Gabriels in later years, such as at the 1896 Big Horn Mine at Mount Baden-Powell , and the 1913 Allison Mine on Iron Mountain high above the East Fork, where several tunnels of up to 1,000 feet (300 m) in length remain. Settlements of considerable size were established in very rough country along the upper San Gabriel River. Prospect Bar, located 4 miles (6.4 km) up the narrow canyon of

3549-479: The Spanish. Disease severely reduced the native populations, and by the beginning of the 19th century, most of the surviving Gabrieliño had entered the mission system. In 1830, nine years after California had become a part of Mexico , the indigenous population had fallen to about a quarter of what it had been before Spanish colonization. In order to attract settlers to the region, Spain and later Mexico established

3640-480: The Tongva described them as a peaceful people. Anthropologists believe the Tongva may have been some of the more advanced native inhabitants of California, establishing currency and complex trade systems with neighboring tribes, cultivating trees and plants for food, and having a formal government structure. Indian Agent B.D. Wilson wrote in 1852 the Tongva knew "how to meet the environmental challenge without destroying

3731-470: 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

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3822-622: The alluvial slope were poorly-defined at best and frequently changed course with winter storms, leaping back and forth between several different ocean outlets. In some years it joined with the Rio Hondo , which flows parallel to the San Gabriel and also passes through the Whittier Narrows , and flowed into the Los Angeles River; in others it would swing south toward either Alamitos Bay or Anaheim Bay , or even east towards

3913-527: The aquifer was quite pressurized and close to the surface; natural artesian wells existed in many places. At the southern end of the San Gabriel Valley, groundwater rose to the surface due to the damming effect of bedrock at the Whittier Narrows and formed a perennial stream that ran across the coastal plain to the Pacific. In the 19th century, irrigated agriculture was developed on a large scale in

4004-463: The area although people from some other groups, such as the Chumash, were also present at the San Gabriel mission. Native Americans fleeing the mission system took refuge in the upper canyons of the San Gabriel River where a significant resistance movement persisted for many years. This culminated in the San Gabriel mission uprising in 1785, led by Tongva medicine woman Toypurina , ultimately crushed by

4095-630: The arrival of Spanish explorers in the region, the native population is estimated at 5,000–10,000. Mount San Antonio provided a visual reference for the boundary of the Tongva (Gabrielino) people in the west and the Yuhaviatam people to the east. Most of the San Gabriel River lay in traditional Tongva territory, although the Chumash (who inhabited areas further west) also used the area. Tongva villages such as Puvunga were located on high ground above

4186-534: The availability of space in the downstream channels. Below the Whittier Narrows Dam, the river flows south-southwest across the coastal plain, roughly defining the border of Los Angeles County and Orange County . It flows through Whittier and Pico Rivera and under the Interstate 5 to Downey , where the river becomes a concrete channel. It turns due south, crossing under Interstate 105 and

4277-444: The best quality, differ very much as regards to the richness of the mine. The Crab Hollow diggings are now considered the best and will pay from two to five cents to the pan. The river remained quiet for a number of years, as drought conditions reduced streamflow and made placer mining difficult. The winter of 1858-59 was a wet one, and soon hundreds of gold seekers from both Los Angeles County and Kern County further north descended on

4368-435: The coastal plain, had the highest population density. Villages in the San Gabriel Valley included Alyeupkigna , Amuscopopiabit, Awingna , Comicranga, Cucamonga , Guichi, Houtgna , Isanthcogna , Juyubit , Perrooksnga, Sibagna , and Toviseanga . The village of Sejat was located at the Whittier Narrows. Puvugna was situated around present-day Long Beach , near the river's mouth. The first explorers to make contact with

4459-525: The coastal plain. California became a U.S. state in 1850, two years after the Mexican–American War . One of the decisive battles of the war was fought on January 8, 1847 on the San Gabriel River, which was the last line of defense for Mexican Californio forces led by Mexican Governor-General José Flores , tasked with defending the pueblo of Los Angeles. American forces, led by General Stephen W. Kearney under Commodore Robert F. Stockton , crossed

4550-539: The crest of the range between Mount Islip and Mount Hawkins, more than 7,000 feet (2,100 m) above sea level. Cedar Creek flows south from Windy Gap , 7,588 feet (2,313 m), 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 4.5 miles (7.2 km) past Valley of the Moon Plantation, forming

4641-510: The deepest layers are up to 4 billion years old. However, the uplift of the present mountain range did not start until about 6 million years ago. The mountains are still rising as much as 2 inches (51 mm) per year due to tectonic action along the San Andreas Fault. The Puente and Montebello hills are even younger, no more than 1.8 million years old. As the hills formed, the San Gabriel River maintained its original course, cutting

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4732-608: The earliest human civilizations. The present consensus is that "alluvium" refers to loose sediments of all types deposited by running water in floodplains or in alluvial fans or related landforms . However, the meaning of the term has varied considerably since it was first defined in the French dictionary of Antoine Furetière , posthumously published in 1690. Drawing upon concepts from Roman law , Furetière defined alluvion (the French term for alluvium) as new land formed by deposition of sediments along rivers and seas. By

4823-520: 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

4914-426: The east and west of the San Gabriel Canyon mouth. Rancho San Francisquito , Rancho Potrero Grande , Rancho Potrero de Felipe Lugo , Rancho La Puente , and Rancho La Merced were located further south in the San Gabriel Valley. Rancho Paso de Bartolo was situated in the Whittier Narrows area, and Rancho Santa Gertrudes , Rancho Los Coyotes , Rancho Los Cerritos and Rancho Los Alamitos occupied various areas of

5005-548: The east, before passing under SR 60 . The river then enters the Whittier Narrows , the natural water gap between the Puente and Montebello Hills that forms the southern entrance to the San Gabriel Valley. Here it is impounded by the Whittier Narrows Dam , which serves primarily for flood control. The Rio Hondo also flows through the Whittier Narrows, to the west of the San Gabriel. The Rio Hondo drains most of

5096-417: The environment." The abundant water available in the San Gabriel River basin, a rarity in arid Southern California, was noted by early Spanish explorers and made it an attractive place for Europeans to settle later on. Juan Rodriguez Cabrillo sailed past the mouth of the San Gabriel River in 1542; although he did not land here, he did make contact with the native Tongva, who rowed out in their canoes to greet

5187-719: The expedition. The first Spanish party to actually cross the river was the Portolà expedition , led in 1769 by Captain Gaspar de Portolà . Juan Crespí , a missionary traveling with the expedition, described their first impression of the San Gabriel River: We then descended to a broad and spacious plain ... After traveling for an hour through the valley we came to an arroyo of water which flows among many green marshes, their banks covered with willows and grapes, blackberries, and innumerable Castilian rosebushes ... It runs along

5278-417: 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. The East Fork , 17 miles (27 km) 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

5369-472: The foot of the mountains, and can be easily used to irrigate the large area of good land ... The valley ... is surrounded by ranges of hills. The one to the north is very high and dark and has many corrugations, and seems to run farther to the west. The expedition had to build a bridge across the river because the channel was too swampy and muddy, making it difficult to move their horses and supplies. The area came to be known as "la puente" (the bridge), from which

5460-507: The foothill zones, chaparral and brush dominate. The Puente Hills , which bisect the lower San Gabriel watershed, contain some sensitive plant communities such as coastal sage scrub and walnut forests. Wildfires are a natural part of plant communities in the San Gabriel River watershed. After the flood of 1938, an intense program of wildfire suppression began, since burned areas tend to erode quickly during storms, causing landslides and mudflows down tributary canyons. Like many other areas of

5551-421: The front range of the San Gabriels to form the flat valley floor. In the San Gabriel Valley, riverine alluvium deposits can be up to 10,000 feet (3,000 m) deep. On the coastal plain, San Gabriel River sediments are interbedded with those from the nearby Los Angeles River as well as marine sediments left behind from ancient sea level changes. Prior to the development of the floodplain, the river channels down

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5642-602: The largest Tongva villages, Asuksangna (meaning "place of the grandmothers") was located at the mouth of the San Gabriel Canyon. The West Fork of the San Gabriel River Canyon formed part of a trade route that crossed the San Gabriel Mountains, enabling the Tongva to trade with the Serrano people in the Mojave Desert to the north. Many other villages were located near the San Gabriel River. The San Gabriel Valley, with its fertile soils and higher rainfall than

5733-543: The largest wildfire in Los Angeles County's history, was mostly concentrated west of the San Gabriel watershed, but did burn much of the upper West Fork. With urban development expanding toward mountain areas, the threat of property damage continues to increase. The San Gabriel River historically supported large populations of native fish, including the largest runs of steelhead in Southern California. Steelhead once migrated over 60 miles (97 km) upriver from

5824-408: The late 19th century. "Colluvium" is now generally understood as sediments produced by gravity-driven transport on steep slopes. At the same time, the definition of "alluvium" has switched back to an emphasis on sediments deposited by river action. There continues to be disagreement over what other sediment deposits should be included under the term "alluvium". Most alluvium is Quaternary in age and

5915-573: The main cause can be attributed to urban and suburban development. This is because such land use has a domino effect that can be felt tens of kilometers away. Consistent decrease to ecological health of streams can be from many things, but most can be directly or indirectly attributed to human infrastructure and action. Urban streams tend to be "flashier" meaning they have more frequent and larger high flow events. Urban streams also suffer from chemical alterations due to pollutants and waste being uncleanly dumped back into rivers and lakes. An example of this

6006-564: The mission was soon attached to the river as well as the San Gabriel Mountains, which had been previously called the Sierra Madre by the Spanish. The original site suffered chronic flooding and was moved to its present site in San Gabriel , 5 miles (8.0 km) northwest, in 1775. The mission eventually controlled 1,500,000 acres (610,000 ha) of land extending from the foot of the mountains as far as present-day San Pedro . Under

6097-526: The modern-day city of La Puente takes its name. Following the Portolà expedition, Spain claimed California as part of its empire, and the San Gabriel River was referred to as "Río San Miguel Arcángel". Mission San Gabriel Arcángel , the fourth in a chain of missions along the California coast, was founded in 1771 by Junípero Serra , along the San Gabriel River near present-day Montebello . The name of

6188-522: The mountains into the San Gabriel Valley, ranging from fine sands, gravels, clays, and silt to car-sized boulders. Starting in the Pliocene , about 5 million years ago, the Los Angeles Basin experienced considerable tectonic subsidence; at the same time, the San Gabriel River was depositing a huge alluvial fan , essentially an inland delta, radiating from the mouth of San Gabriel Canyon. This has combined with smaller alluvial fans from other drainages along

6279-591: The mountains, most of the streams are locked in artificial channels, and the vast majority of the original wetlands have been lost to urban development. Less than 2,500 acres (1,000 ha) of wetlands remain in the San Gabriel River watershed, with the greatest decline in the coastal floodplain zone. Most remaining wetland habitats are either immediately adjacent to the river, or within the Whittier Narrows and other flood control basins, providing habitat to birds and small mammals. In addition, riparian and wetland restoration projects have been completed or are in progress along

6370-421: The north, and then the much larger Bear Creek, which originates at Islip Saddle near the 8,250-foot (2,510 m) 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. The North Fork is the shortest and steepest of the three major forks. It begins as a series of streams falling off

6461-489: 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 120-foot (37 m)-high 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

6552-472: The policy of reducción , the purpose being to "reduce or consolidate the Indians from the countryside into one central community", the Spanish incentivized Native Americans to joining the mission system first via gifts, but also often by force. Native people worked on farms and ranches of the mission lands, and were converted to Christianity. The Spanish name "Gabrieliño" generally refers to the Tongva people of

6643-418: The problems caused by alteration, using techniques such as daylighting and fixing stream bank erosion caused by heavy stormwater runoff. Streamflow augmentation to restore habitat and aesthetics is also an option, and recycled water can be used for this purpose. Urban stream syndrome (USS) is a consistent observed ecological degradation of streams caused by urbanization. This kind of stream degradation

6734-494: The reach of winter floods. A typical village consisted of large, circular thatched huts known as "kich" or "kish", each home to multiple families. During summer, the villagers would travel up the San Gabriel Canyon into the mountains to gather food and other resources needed to pass the winter. The San Gabriel River itself also provided sustenance to Native Americans with its steelhead trout and game animals attracted by this rare permanent water source. The abundant plant life around

6825-404: The river and its marshes, especially tule , were used to build dwellings and canoes. The Tongva often set brush fires to clear out old growth, improving forage for game animals. They also made oceangoing canoes (ti'at) using wooden planks held together with asphaltum or tar from local oil seeps . At least 26 Tongva villages were located along the San Gabriel River, and another 18 close by. One of

6916-693: The river bed reverts from concrete to earth. It passes under Interstate 405 and SR 22 , past Leisure World and Joint Forces Training Base - Los Alamitos (Los Alamitos Army Airfield), and under the Pacific Coast Highway . It empties into the Pacific Ocean between Alamitos Bay and Anaheim Bay (to the south), on the boundary of Long Beach in Los Angeles County, and Seal Beach in Orange County. The San Gabriel River, its canyons, and its floodplain are relatively young in geological terms, and owe their existence to tectonic forces along

7007-674: The river under heavy fire, but were able to force the Californios from their defensive position in under ninety minutes. After taking control of the river, the Americans were able to take Los Angeles on January 10, and the Mexicans surrendered California three days later. This campaign is now remembered as the Battle of Rio San Gabriel . Although it was rumored for many years that Native Americans and Spanish explorers had discovered gold in

7098-477: 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

7189-423: The river. By May 1859, claims were staked along 40 miles (64 km) of the San Gabriel Canyon. In the early days, access to the diggings proved difficult, as the rocky San Gabriel River bed was the only way into the rugged mountains. In July 1859, stagecoach service was established to bring in miners and their supplies. Between 1855 and 1902, an estimated $ 5,000,000 ($ 153 million in 2023 dollars) worth of gold

7280-458: The river. The San Gabriel River Wetland Restoration Development intends to construct by 2018 an artificial wetland and bioswale system near El Monte which will provide a recreation area and wildlife habitat and buffer against pollution. Above elevations of 7,000 feet (2,100 m), the San Gabriel Mountains support some pine and fir forests, remnants or relicts of a huge evergreen (coniferous) forest that once covered Southern California during

7371-406: The south. At its mouth, the river emptied into a broad estuary surrounded by thousands of acres of permanent marsh and swamp land, the result of a band of bedrock running parallel to the coast, forcing groundwater to the surface. In mountain areas, the San Gabriel River channel is often too narrow to support significant vegetation, as winter floods tend to scour the channel down to bare rock. Below

7462-560: The stream into culverts and storm sewers , or other means. Some urban streams, such as the subterranean rivers of London , run completely underground. These modifications have often reduced habitat for fish and other species, caused downstream flooding due to alterations of flood plains , and worsened water quality . Toxicants , ionic concentrations, available nutrients , temperature (and light), and dissolved oxygen are key stressors to urban streams. Some communities have begun stream restoration projects in an attempt to correct

7553-426: The symptoms, most commonly through channel reconfiguration that includes reshaping rock to address altered hydrology and sediment regimes. In spite of having ecological objectives, this approach has been criticized for addressing physical failures in the system without improving ecological conditions. Alluvium Alluvium (from Latin alluvius , from alluere  'to wash against')

7644-477: The two rivers sometimes joined the other, flowing to various outlets. The Rio Hondo sometimes changed course to join the San Gabriel River; alternatively, the San Gabriel sometimes shifted course into the Rio Hondo, merging into a single watershed with the Los Angeles River. Whittier Narrows Dam controls the outflow from both rivers into their artificially fixed channels. During storms, water is distributed based on

7735-651: 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

7826-512: The water gap of the Whittier Narrows. Composed of ancient, highly fractured and unstable crystalline rock, the San Gabriel mountains are subject to tremendous amounts of erosion. Rapid erosion caused by heavy winter storms has created the dramatic canyons of the San Gabriel River. In the headwaters, streams often follow fault traces; the West Fork and part of the East Fork run along the San Gabriel Canyon Fault, which extends in

7917-458: 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

8008-505: The western United States, this has caused a large amount of tinder and debris to accumulate, increasing the risk of fire. Drought conditions in the first decade of the 21st century led to huge fires much larger than would have occurred naturally. In 2002, the Curve Fire burned 20,000 acres (8,100 ha), much of it in the North Fork of the San Gabriel River, closing Crystal Lake Recreation Area for several years. The 2009 Station Fire ,

8099-409: The western half of the San Gabriel Valley, approaching the San Gabriel River at the Whittier Narrows; south of there, it swings to the southwest and joins the Los Angeles River . In the Whittier Narrows, they are connected by a short channel through which water can flow in both directions. The Rio Hondo is generally considered a separate stream and tributary to the Los Angeles River , but historically

8190-502: Was removed from the San Gabriel River. Mining along the San Gabriel River began with simple gold panning, but soon developed to more advanced methods. Flumes were constructed to carry water to sluices , long toms, and hydraulic mining operations that separated gold from river gravel; dams and waterwheels helped maintain the necessary head to drive these extensive waterworks and clear the riverbed so that gold-bearing sands could be excavated. Some hard rock (tunnel) mining also occurred in

8281-428: 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. 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,

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