| San Andreas Creek[1] San Andrés Creek,[2] | |
|---|---|
 San Andreas Creek'sSan Andreas Reservoir | |
 | |
| Etymology | Saint Andrew |
| Location | |
| Country | United States |
| State | California |
| Region | San Francisco Peninsula |
| County | San Mateo County |
| Physical characteristics | |
| Source | East slope ofSweeney Ridge[3] |
| • coordinates | 37°37′01″N122°27′29″W / 37.61694°N 122.45806°W /37.61694; -122.45806 |
| • elevation | 918 ft (280 m) |
| Mouth | Confluence with Lower Crystal Springs Reservoir (originally withSan Mateo Creek) |
• location | Pacifica, California |
• coordinates | 37°36′50″N122°26′28″W / 37.61389°N 122.44111°W /37.61389; -122.44111 |
• elevation | 285 ft (87 m) |
San Andrés Creek (Spanish for:St. Andrew's Creek), now calledSan Andreas Creek, is a perennial stream that flows 5.9 miles (9.5 km)[3] southeasterly along theSan Andreas Fault fromSweeney Ridge inSan Mateo County, California, providing the inflow to and outflow fromSan Andreas Reservoir, and then enteringLower Crystal Springs Reservoir, where it was a historic tributary toSan Mateo Creek. San Mateo Creek then carries its waters overCrystal Springs Dam northeast toSan Francisco Bay.
After discovering San Francisco Bay fromSweeney Ridge on November 4, 1769, thePortolà expedition descended whatPortolà called theCañada de San Francisco, now known asSan Andreas Creek, to camp just south of the San Mateo Creek canyon on a lake called by himLaguna Grande, now covered byUpper Crystal Springs Reservoir. The campsite is marked by California Historical Marker No. 94 "Portola Expedition Camp".[4] After heading south and descending from the foothills alongSan Francisquito Creek to established his base camp atEl Palo Alto, Portola retraced his steps and returned along San Andreas Creek to recross Sweeney Ridge and then via the coast back toSan Diego. TheSan Andres Creek place name is shown on theRancho de las Pulgas 1856 plat map.[5][6]Padre Palóu, on an expedition from Monterey to explore the western side of San Francisco Bay led byCaptain Rivera, renamed Portola'sCañada de San Francisco toCañada de San Andrés on November 30, 1774, it being the feast day ofSt. Andrew.[7]Captain Juan Bautista de Anza, after forging the first overland route fromMonterey, California, to San Francisco Bay, explored the peninsula and selected the sites for theMission San Francisco de Asís (Mission Dolores) and thePresidio of San Francisco. De Anza returned to Monterey via theCañada de San Andrés and camped on the banks ofSan Mateo Creek on March 29, 1776. In de Anza's diary on March 29, 1776, he wrote: "Night having fallen, at a quarter past six I went down to the arroyo of San Andreas and to another, that of San Matheo, where it descends to empty into the estuary."[8]
The two Crystal Springs lakes and San Andreas Lake used to be known asSpring Valley Lakes for the Spring Valley Water Company which owned them. The Spring Valley Water Company named the lakes, the Spring Valley Lakes, after the company. The original Spring Valley was between Mason and Taylor Streets, and Washington and Broadway Streets inSan Francisco, where the water company started. When the company went south for more water, the Spring Valley name was carried south too.[9]
San Andreas Creek's source elevation is at approximately 900 feet (270 m) on the eastern slopes ofSweeney Ridge from which it flows southeasterly along theSan Andreas Rift betweenSweeney Ridge to the west andBuri Buri Ridge to the east, throughSan Andreas Reservoir, which was formed by the construction of a 100-foot-high (30 m) earth dam in 1868.[2][10] The San Andreas Dam eliminates flow in the creek immediately below the dams, except for occasional spills or releases from the reservoir and seepage through the dam.[11] From San Andreas Reservoir, the creek descends and enters the northeast arm ofLower Crystal Springs Reservoir. Historically San Andreas Creek joined San Mateo Creek just above the current location of theCrystal Springs Dam. The two Crystal Springs lakes and San Andreas Lake used to be known asSpring Valley Lakes for the Spring Valley Water Company, which owned them. Lower Crystal Springs Reservoir now covers the town ofCrystal Springs, which grew up around a resort of the same name.[12][13]
Before European settlers arrived, much of the San Andreas Valley portion of the watershed was composed ofwetlands. Wetlands are habitats that are a combination water-submerged land, and land that floats above the water. They have several different categories, which are distinguished by the type of water (freshwater, saltwater, etc.) and the type of land (marshes,mangroves, etc).[14] San Andreas Creek was lined with several, relatively smallsag ponds, which are bodies of water formed by fault line movements that create basins where freshwater can collect.[15] These aquatic habitats allowedriparian (referring to the banks of bodies of water) wildlife to thrive. However, the arrival of colonizers between the late 18th and mid 20th centuries led to a string of impactful environmental and ecological changes to San Andreas Creek and the rest of the watershed. For instance, several dams were built, including the San Andreas Dam, and theUpper and Lower Crystal Springs Dams. These dams completely deluged the naturally existing aquatic habitats, including the riparian ones, desiccating much of the wildlife. However, for a period of time before the 20th century, the existinggrassland habitats seemed to increase, whileshrubland area decreased, as a result of the farming practices introduced by the Spanish, and the forced termination of Indigenous burning practices. However, modern American influences from the mid 20th century onwards have decreased the grassland area by about 70%, and this destruction was accelerated by highway construction and residential development. These haven't been the only habitats to face destruction around the San Andreas creek and the surrounding area; furthermore, other environmental damages, such asSudden Oak Death and the spread of plant pathogens, have exacerbate as a result of various human-created developments. In response, there have been efforts to restore several original habitats, including wetlands, grasslands, and others.[16]
Fog drip may play a key role in the precipitation in the upper watershed. On Cahill Ridge (just west of San Mateo Creek and east ofPilarcitos Creek, at an elevation of 1,000 feet (300 m), Oberlander measured fog drip beneathtanoak (Lithocarpus densiflorus), Coast redwood and three Douglas fir trees, the latter 125 feet (38 m) tall. He found that the trees most exposed produced the most precipitation and in five weeks of measurement (July 20 – August 28, 1951) fog drip below the tanoak produced 59 inches (1,500 mm) of precipitation, more than the total annual precipitation on nearby grasslands and chaparral. The Douglas fir produced 7 to 17 inches (180 to 430 mm) of fog drip and appeared to provide unique conditions supporting the orchidsgiant helleborine (Epipactis gigantea) andphantom orchid (Cephalanthera austiniae), since these plants were found exclusively in these moist ridge tops.[17]
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