San Mateo Creek is a stream in Southern California in the United States, whose watershed mostly straddles the border of Orange and San Diego Counties. It is about long, flowing in a generally southwesterly direction. Draining a broad valley bounded by the Santa Ana Mountains and Santa Margarita Mountains, San Mateo Creek is notable for being one of the last unchannelized streams in Southern California.
One of the least developed watersheds on the South Coast, San Mateo Creek's drainage basin covers in parts of the Cleveland National Forest and Marine Corps Base Camp Pendleton. The first inhabitants were Native Americans primarily of the Acjachemen and Luiseño groups, followed by the Spanish who established ranchos in the area. The creek's usually perennial flow made it an important source of irrigation water, then in the later 19th century, there was a gold rush in the upper watershed. Most of the little development in the watershed was agriculture-based.
The San Mateo Creek watershed includes the subwatersheds of Los Alamos Canyon Creek, Tenaja Canyon Creek, Devil Canyon Creek and Cristianitos Creek with its tributaries of Talega and Gabino Creeks. Although grazing activities have hurt the biological quality of the semi-arid, Mediterranean-climate watershed, it still supports numerous biological communities including riparian zones, grassland and coastal sage scrub. A population of steelhead trout was identified in the creek in 2007, which population is adversely affected by continuing groundwater pumping, and which also may have been minimally impacted by minor agricultural runoff prior to cessation of farming activities along the stream aboard Marine Corps Base Camp Pendleton.
Course The -long San Mateo Creek begins its course in a canyon in the extreme southeastern end of the Santa Ana Mountains, which lie mostly in Riverside County. From there, the creek continues through a steep and narrow gorge for the first part of its course, then a broad and shallower valley for the second part. It receives four major tributaries and many smaller ones on its generally southwest journey to the Pacific Ocean.
San Mateo Creek has its source, at an elevation of 2800 feet, Beatrice Dawson Wood, Water Supply paper 297; Gazetteer of Surface Waters of California, Pt. 3, Pacific Coast and Great Basin streams, U.S. Government Printing Office, Washington, 1913, p.190 in the canyon on the west face of the unofficially named 3,591 ft. San Mateo Peak,Lower Peaks Committee, Angeles Club, Sierra Club, Sierra Club Lower Peaks Committee Guide, 2009 edition, Lower Peaks Committee, Fullerton, 2009 at the western end of the ridge running west then northwest from Elsinore Peak to Morrell Canyon, south and west of the Morrell Potrero in the Elsinore Mountains. From its headwaters south of Lake Elsinore inside the Cleveland National Forest, San Mateo Creek runs southwards through the valley of the old Rancho at the Potrero de la Cienaga which as its name suggests feeds the creek with several springs. The canyon widens and deepens until it is roughly in depth. After running south for several miles it turns southeast to the Tenaja Falls where it tumbles down to its confluence with Los Alamos Canyon Creek, that comes in from the left. This creek with its tributary Wildhorse Canyon Creek and two unnamed arroyos drain the southern slopes of Elsinore Peak. Another unnamed arroyo drains the western Santa Rosa Plateau and the east slope of the Tenaja Mountain highland and descends to the north to join the creek where it turns to the west.Unnamed arroyo draining east slope of the Squaw Mountain highland and western Santa Rosa Plateau, USGS Map Name: Wildomar, CA, Map Center: from topoquest.com accessed on 5/4/2013
From its confluence with Los Alamos Canyon Creek, San Mateo Creek turns its course southwest down San Mateo Canyon, cutting a deep arid canyon surrounded by slopes dissected by many side canyons between the Santa Ana and Santa Margarita Mountains. USGS Map Title: Wildomar, CA, from topoquest.com accessed on 4/16/2013 USGS Map Name: Sitton Peak, CA, from topoquest.com accessed on 4/16/2013 At river mile (RM) 18 or river kilometer (RK) 28.9, Tenaja Canyon Creek, which flows generally northwest, comes in from the left. Shortly after, at RM 17.5 (RK 28.1) Bluewater Canyon Creek descends from Sitton Peak, to merge with San Mateo Canyon from the right. Nickel Canyon Creek also comes in from the right, descending from the Verdugo Potrero shortly afterward, joining San Mateo Creek just north of the Riverside – San Diego County line.
The creek then continues to flow southwards and Devil Canyon Creek draining the eastern slope of the Santa Margarita Mountains with its tributary, Cold Spring Canyon Creek, comes in from the left at RM 15 (RK 24.1). The Devil Canyon Creek confluence approximately marks the point where San Mateo Creek leaves the Cleveland National Forest. Soon, the narrow -deep canyon gives way to a broad alluvial valley. San Mateo Creek flows past Camp Pendleton, a United States Marine Corps amphibious training base. At RM 3.7 (RK 5.95) Cristianitos Creek, the largest tributary, joins from the right. Cristianitos Creek begins in extreme southeastern Orange County and drains about , that includes its tributaries of Talega Canyon Creek and Gabino Canyon Creek and its tributary La Paz Canyon Creek that enter it from the left.
San Mateo Creek then crosses under Interstate 5 and the Trestles Bridge which carries the Surf Line and empties into a small, perennial freshwater lagoon bounded by a sandbar at San Onofre State Beach. The lagoon only empties into the sea during the rainy season. This portion of the creek is very close to San Clemente and a small residential area is just to the northeast side of the lagoon. The lagoon remains similar to its natural state as well, although it is increasingly becoming harmed by unnatural pollutants.
Geologic history Geologically the San Mateo Creek watershed is dominated by the Santa Ana Mountains, whose underlying bedrock consists of Jurassic-age igneous and sedimentary rock, overlain by a few thousand vertical feet of Cretaceous-age granite, gabbro, and tonalite. Underneath the San Mateo Creek valley's several hundred feet of alluvial deposits, there are layers of sandstone, limestone, siltstone, mudstone, shale and conglomerate. These formations are present along most of the streams draining off the west slope of the Santa Ana Mountains and are practically identical as far north as Santiago Creek, which is in north-central Orange County nearly away.
The alluvial deposits originate from the Wisconsinian glaciation, in which massive glaciers and ice sheets advanced over much of North America and shifted the global climate. During this roughly 60,000-year-long period that ended in approximately 8000 B.C., Southern California received up to of rainfall per year, and this radical climate change coincided with a drop in sea level. As the sea levels fell, streams flowing into the Pacific from Southern California began to erode massive canyons in their floodplains.
The rivers eventually eroded to or so below their previous elevation. When the Wisconsinian period ended, sea level rose, filled these canyons and turned them into long, narrow inlets. Because the heavy rains ceased with the departure of the Wisconsinian, the rivers and streams once again became slow-flowing. Over the course of thousands of years, these calm inlets gradually filled with alluvial sediments, giving them the flat valley floors they have today. Over time, sea level dropped slightly again, allowing the rivers to once again entrench channels into their floodplains, resulting in the broad river terraces that line much of lower San Mateo Creek, Arroyo San Onofre and San Juan Creek.
Soils Most of the soils in the San Mateo Creek drainage area are loamy, well-drained and also fertile in the lowlands. In the mountains the soil cover is very shallow and there are many exposed cliffs, large boulders and outcroppings of sedimentary rock. In the lower watershed are sandy or silty loams which have a clay substructure. These soils are classified as highly fertile and there are a few farms on the foothills and the floodplain of the San Mateo Creek watershed.
Watershed
The San Mateo Creek drainage basin covers mostly in San Diego County and partially in Orange County. It shares boundaries with several watersheds – including Segunda Deshecha Cañada to the west, Arroyo San Onofre to the southeast, and streams draining into Lake Elsinore in the northeast. It is slightly larger than the San Juan Creek watershed, which borders on the San Mateo Creek watershed's northeastern side.
The upper reaches of the watershed consist primarily of canyons that are deep and broad, while the lower watershed is a valley wide and less than deep. The largest tributary of San Mateo Creek is Cristianitos Creek (in Christianitos Canyon), which is about long and with its tributaries, drains in the western portion of the watershed with a portion in Orange County. Other significant sub-basins in the watershed include Talega Canyon, La Paz Creek and Gabino Creek, all of which are tributaries of Cristianitos Canyon.
The Santa Ana Mountains form the drainage divide with San Juan Creek on the northwest side of the San Mateo Creek valley, and the Santa Margarita Mountains on the southeast separate San Mateo Creek from the Arroyo San Onofre, a creek that drains westwards to the Pacific Ocean. Arroyo San Onofre is also the closest major stream to San Mateo Creek by location of the mouth. The next closest is Segunda Deshecha Cañada, further north. Much of the upper San Mateo Creek watershed is encompassed by the central Cleveland National Forest and the lower lies mostly within Camp Pendleton. The closest city is San Clemente, northwest of the creek's mouth.
San Mateo Creek was once a seasonal stream that would flow through the rainy season, run dry by June or July and restart in October. Although springs exist in the mountains, once the creek spilled onto its floodplain, it would seep into the ground and run in a subsurface manner. Irrigation return flows and a sewage treatment plant have increased its flows to perennial, although it does not receive as much runoff as most other Southern California streams. The typical annual peak flow is around , while the 2-year flood is , the 10-year event, , and the 100-year flood, .
Ecology
Plants Supporting a highly productive ecosystem, the San Mateo Creek watershed includes a high variety of elevations and vegetation groups. These include riparian zones and woodlands around the perennial or semi-perennial streams, grassland on the valley floors, and chaparral and coastal sage scrub on the hillsides. Overall the vegetation groups and their distribution are very similar to that of San Juan Creek and its major tributary, Trabuco Creek, in the northwest. The major difference is that the San Mateo Creek watershed contains no major residential areas.
The mouth of the creek and its last reaches shortly above and below Camp Pendleton are host to a wide variety of riparian plants. At the mouth, there is a freshwater lagoon and several freshwater marshes, surrounded by a riparian woodland consisting primarily of willow, sycamore, live oak and cottonwood. Surrounding the lower San Mateo Creek valley and on the shallow slopes is the coastal sage scrub community, which consist primarily of coast goldenbush, coyote brush, California sagebrush, mulefat, toyon, poison oak, laurel sumac, California mugwort, Mexican elderberry, and California encelia. At the very mouth, where groundwater surfaces on the streambed, there are the stands of trees, and undergrowth includes wild cucumber and gooseberry.