page_title: San Mateo Creek (Southern California)
section_title: Course
hierarchical_section_title: San Mateo Creek (Southern California) / Course
caption_attribution_description: English: San Mateo Creek at intersection with Tenaja Truck Trail near the Tenaja Falls Trailhead, Cleveland National Forest, California, USA
context_page_description: 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 22 miles 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 139 square miles 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 is now 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.
context_section_description: The 22-mile (35 km)-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, in the canyon on the west face of the unofficially named 3,591 ft. San Mateo Peak, 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 600 feet (180 m) 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 Squaw Mountain highland and descends to the north to join the creek where it turns to the west.
  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.  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 2,500-foot (760 m)-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 29 square miles (75 km²), 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 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.
caption: San Mateo Creek at Tenaja Truck Trail crossing near Tenaja Falls Trailhead
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