Arroyo Seco (Los Angeles County)

TheArroyo Seco, meaning "drystream" inSpanish, is a 24.9-mile-long (40.1 km)seasonal river, canyon,watershed, and cultural area inLos Angeles County, California. The area was explored byGaspar de Portolàwho named the stream Arroyo Seco as this canyon had the least water of any he had seen. During this exploration he met the ChiefHahamog-na(Hahamonga) of theTongvaIndians.
The watershed begins atRed Box Saddlein theAngeles National ForestnearMount Wilsonin theSan Gabriel Mountains. As it enters the urbanized area of the watershed, the Arroyo Seco stream flows betweenLa Cañada Flintridgeon the west andAltadenaon the east. Just below Devil's Gate Dam, the stream passes underneath theFoothill Freeway. At the north end ofBrookside Golf Coursethe stream becomeschannelizedinto aflood control channeland proceeds southward through the golf course.
The Arroyo Seco goes throughPasadena, where it passes theRose Bowl Stadiumas it goes through Brookside Park.The Arroyo Seco stream, which is fed by a watershed of 46.7 square miles (121.0 km), helps to replenish the Raymond Basin, an aquifer underlying Pasadena that provides about half of the local water supply. This arroyo is one of two major streams that capture rainfall and storm water in Pasadena, the other beingEaton Washon the eastern side of the city, which is a tributary of theRio Hondowatershed.
The Arroyo Seco then passes under theVentura Freewayand theColorado Street Bridge, and it crosses theRaymond Faultat the southern boundary of Pasadena at theSan Rafael Hills. The channel continues along the western boundary ofSouth Pasadena, then into northeast Los Angeles flowing southeast of theVerdugo MountainsandMount Washington.
The Arroyo Seco then proceeds through theLos Angeles neighborhoodsofHighland Park,Hermon,Montecito Heights, andCypress Park. It ends at theconfluencewith theLos Angeles RivernearElysian Park, north ofDodger StadiumandDowntown Los Angeles.
TheArroyo Seco Parkway, or Pasadena Freeway, runs parallel to the channelized Arroyo Seco from South Pasadena to the Los Angeles River.
Above Devil's Gate, the rapids of the Arroyo Seco are positioned so that the falls make a beating, laughing sound. InTongva-Gabrieliño traditional narratives, this is attributed to a wager made between the river and thecoyote spirit.
The Arroyo Seco was one of the Los Angeles River tributaries explored by Gaspar de Portola in the late summer and fall of 1770. He named the stream Arroyo Seco, for of all the canyons he had seen, this one had the least water. During this exploration he met the ChiefHahamog-na(Hahamonga) near Millard Canyon, at the settlement later known asHahamongna, California. This band of theTongvaIndians would end up gathered into the fold of theSan Gabriel Missionand with other bands and tribes collectively called "Gabrielenos".
The Arroyo Seco region can be considered by historical accounts as the birthplace of Pasadena. After the 1820s secularization of the Missions, the broad area to the east of the Arroyo was theMexican land grantofRancho San Pascual, present-dayPasadena, California.Manuel Garfiaswas the grantee of the Rancho and its longest early resident. Hisadobehouse was on the east ridge of the Arroyo, in present-daySouth Pasadena.
With the 1874 establishment of the community of theIndiana Colony, the new residents built their homes along today's Orange Grove Boulevard, the major north–south avenue paralleling the Arroyo on the east. However, the deep and seasonally flooded Arroyo presented a barrier to easy travel and transportation between renamed Pasadena and Los Angeles. Stories of four and five hours just crossing the chasm, whether exaggerated or not, abounded in Pasadena history.
The first recorded American to live in the Upper Arroyo (north of Devil's Gate) was simply known as "Old Man Brunk". Brunk's cabin stood at a large bend in the canyon, roughly where the Forest Service housing is today. It was said he leftSan Francisco"for that town's good".
Dating back to the originalTongvaresidents of the area, the Arroyo Seco canyon has always served as a major transportation corridor.  Today it links downtown Los Angeles with Pasadena, the westSan Gabriel Valleyand theSan Gabriel Mountains.
By 1886 theLos Angeles and San Gabriel Valley Railroadhad been established from Downtown Los Angeles with a grand wooden trestle that cut a straight line crossing from the west side to the east. The wooden trestle was replaced with theSanta Fe Arroyo Seco Railroad Bridge. Eventually this line would hook up with rail lines built from the east to create the cross-country course of theSanta Fe Railroad. For local commutes, an electric traction trolley was put in and operated by thePacific Electric Railway, aHenry E. Huntingtonenterprise, which ran the "Red Cars" from the upper Arroyo and Pasadena through the San Gabriel Valley into Los Angeles and many points beyond.The lower Arroyo Seco was served by theLos Angeles Railway"Yellow Car" lines.
In 1900Horace Dobbins, Mayor of Pasadena, opened his innovativeCalifornia Cycleway, an elevated wood structure with a flat planked surface that would allow bicyclers to travel from Pasadena to Los Angeles avoiding the uncertain schedules of the early trains. Dobbins was only able to build a two-mile portion of the cycleway from the Green Hotel to Raymond Hill before competition from the railroads and the growing popularity of thehorseless carriageundermined the project. Present day cycling activists are reviving a vision and plan for adedicated bikewayfrom Pasadena to Los Angeles.TheArroyo Seco bicycle pathnow runs from Highland Park to South Pasadena; theKenneth Newell Bikewaycontinues the route through Pasadena.
In 1913 theColorado Street Bridgewas dedicated. This structure curves across the Arroyo accessingEagle Rock,Glendale, and theSan Fernando Valley. During theStock Market Crash of 1929and the subsequentGreat Depressionof the 1930s, the bridge was a jumping off point for many committingsuicide, whereby it received the ignoble name of "Suicide bridge." By the 1980s the bridge fell into disrepair as chunks of concrete dropped from its face to the armory parking lot in the Arroyo below. In October 1989, the Colorado Street Bridge was closed as a precautionary measure in the aftermath of theSan Francisco–Oakland Bay Bridgefailure in theLoma Prieta earthquake. Eventually assistance from the Federal Bridge Repair and Replacement Fund and other local governmental agency discretionary funds provided funding for the complete restoration andseismic retrofitof the bridge. The total project budget amounted to $24 million, and the Colorado Street Bridge was reopened on December 13, 1993, on time and on budget.
By mid-20th Century, the automobile had long become a mainstay of Southern California life. In 1940 theArroyo Seco Parkway, the first freeway, was built as aparkwayalongside the newly constructed flood channel in the Los Angeles portion of the Arroyo. Today, also known as thePasadena Freeway, it continues on through downtown becoming theHarbor Freeway, and terminates near the harbor inSan Pedro.
The Arroyo Seco Corridor Management Plan was completed for the "Arroyo Seco Parkway" in 2004.  The Plan was created through a partnership with theNational Trust for Historic Preservation, theNational Scenic Byways Center(Federal Highways),Caltrans(State Highways), theNational Park Service, theSanta Monica Mountains Conservancy, and The Center for Preservation Education and Planning (CPEP Inc.).
The Arroyo Seco Flood Control Channel, was built by the Works Progress Administration before and during construction of the parkway to avoid damages from future floods.
The Arroyo Seco generally has a flow of several cubic feet per second,but periodically it is inundated by torrential floods from its steep, erosion-prone mountain watershed. The reputation of Arroyo Seco floods led the Spanish to site the originalPueblo de Los Ángelesaway from theconfluenceof the Arroyo Seco and theLos Angeles River. Historically, these floods would race down the stream bed and overflow through Pasadena, South Pasadena, Alhambra and Los Angeles communities all the way to the Los Angeles River. As Los Angeles developed into a city and grew outwards, the damage from these floods was particularly severe in 1914 and 1916.
In 1920(105 years ago)(1920), theLos Angeles County Flood Control Districtbuilt the first flood control dam in Los Angeles County at Devil's Gate gorge.Named for a rock outcropping which resembles the face of a devil, this is the narrowest spot on the Arroyo Seco's course below Millard Canyon. The construction was by theBent Brothers Company. Devil's Gate Dam in the Arroyo Seco in northern Pasadena betweenLa Cañada FlintridgeandAltadenais managed by theLos Angeles County Department of Public Works.
The flood basin above the dam captures the flows of the mountain watershed of the Arroyo Seco. This area is now called "Hahamongna", a phrase meaning "Flowing Waters, Fruitful Valley" in the language of the Tongva tribe who first inhabited the area. In 2011, the flood basin had filled with debris brought down after the 2009Station Fire, reducing its effectiveness as a flood control measure. The County of Los Angeles conducted public hearings on theEnvironmental impact statementbefore selecting a method to remove debris from the Hahamongna area. In 2014, the Board of Supervisors approved a five-year project to remove 2.4 million cubic yards of sediment (1,800,000 m) from the basin despite strong opposition from neighbors and recreational enthusiasts. The opponents contended that hundreds of trucks would be required that would increase pollution and noise.They also said that the wildlife habitat would be destroyed and interfere with hikers, cyclists and horseback riders who use the area for recreation. The alternative supported by Pasadena officials would have removed 1.4 million cubic yards of sediment (1,100,000 m) and provided regular maintenance. County officials supported removing more sediment to reduce the flood risk for most major storms, the work having begun in early-2019.
Below Devil's Gate Dam, most of the Arroyo Seco creek, with two short exceptions, is contained in a concrete channel that contains stormwater and municipal runoff. This channel and other similar flood control structures throughout theLos Angeles Basinand along the foothills of theSan Gabriel Mountainswere built following the devastatingLos Angeles Flood of 1938.
For more than one hundred years, the natural environment of the Arroyo Seco and its proximity to a large urban population have inspired efforts to protect, manage and preserve it.L.A. County flood control was first founded in an effort to control the wild waters of the Arroyo Seco andCharles Lummisfounded the Arroyo Seco Foundation in 1905 for the purpose of preserving recreational use and habitat, residents in Los Angeles and Pasadena contributed generously to efforts to buy up open space in the great canyon to protect for future generations.
There has been a series of studies conducted to assess and improve the management of the Arroyo Seco Watershed.  These include:
The restoration efforts are being carried out by the County of Los Angeles and local cities, primarily the City of Pasadena.
Early rocket-engine-testing began in the Arroyo Seco in 1936 and this led to the establishment of theJet Propulsion Laboratory(JPL) at the mouth of the Arroyo Seco by theCalifornia Institute of Technology.During the 1950s, JPL was heavily involved in rocket testing, and the roar of rocket engines could be heard emanating from the Arroyo Seco area for miles. These rocket projects were terminated at the facility by 1958. By the mid-1960s, JPL had become instrumental in the development, launching, and tracking of a number of unmanned near-Earth and deep-spacespace probesfor theNational Aeronautics and Space Administration. One notable project was theMars rover, which has returned a number of panoramic photos of theMartiansurface.
JPL has been criticized by regional environmentalists and the community for itswater pollutionof the localgroundwaterwithtoxicchemicals, such assolventsandperchloraterocket fuelaccelerants. A monumental cleanup project by NASA has begun, which includes a multimillion-dollar pumping andwater filtrationsystem to treat the groundwater, removing toxins until the aquifer contamination level has been reduced below their federally-specified limits. This project is carried out by a NASA project team and monitored by theU.S. Environmental Protection Agency. Frequent public meetings are held with public comment, and recorded for the record on the quality and progress of the clean-up.
Before channelization, the Arroyo Seco was a spawning habitat for SouthernSteelhead, theAnadromousform of rainbow trout. The Arroyo was home to a resident rainbow trout population until at least 2009, when mudslides following theStation Fire (2009)were thought to have wiped out the population. In November 2020, theCalifornia Department of Fish and Wildlifetransplanted almost 500 trout from theWest Fork San Gabriel River, definitively re-establishing the presence of native trout in the stream.
From mouth to source (year built in parentheses):
To many, the Arroyo Seco is one of the most popular hiking spots in Southern California. The mountainous part of the Arroyo Seco is located within theAngeles National Forest.Angeles Crest Highwayskirts the western edge of the Arroyo Seco Canyon.
The following is a list of Forest Service facilities in the Upper Arroyo, from south to north:
Millard Canyon, located near the mouth of the Arroyo, is a delightful canyon with an impressivewaterfall.  Sunset Ridge The trail skirts the eastern side of the canyon, the eastern boundary of the Arroyo Seco Watershed.  Millard Canyon was a major pedestrian thoroughfare forTongva,Serrano people, and other Californian Native Americans traveling between theLos Angeles Basincoastal plain, theSan Gabriel Mountains, and theMojave Desertregions of Southern California.
Brown Mountain Truck Trail, which begins near the confluence of El Prieto Canyon and proceeds across the front range of the San Gabriel Mountains to upper Millard Canyon, offers impressive vistas of theSan Gabriel Valley.  The Burton Trail descends from this road to the upper stretches of the Arroyo near Oakwilde Campground.
TheGabrielino Trail, which is a popular journey for hikers, equestrians and bicyclists, travels up the steep canyon. A popular hike on the Gabrielino Trail is the 4 mile round trip to lower Switzer Falls from Switzer Picnic area.