|San Luis Rey River|
Mouth of river from N Coast Hwy
|- left||Buena Vista Creek|
|- right||West Fork San Luis Rey River, Pauma Creek|
|- location||Confluence of West Fork San Luis Rey River and Buena Vista Creek, Cleveland National Forest, San Diego County|
|- elevation||2,627 ft (801 m)|
|- location||Oceanside, San Diego County|
|- elevation||0 ft (0 m)|
|Length||69 mi (111 km), East-west |
|Basin||557 sq mi (1,443 km2) |
|- average||36.3 cu ft/s (1 m3/s) |
|- max||25,700 cu ft/s (728 m3/s)|
|- min||0 cu ft/s (0 m3/s)|
The San Luis Rey River is a river in northern San Diego County, California. The river's headwaters are in the Cleveland National Forest near Palomar Mountain. The river drains into the Pacific Ocean on the northern end of the city of Oceanside. The river is over 69 miles (111 km) long and drains 562 square miles (1,460 km2). There is little water in the river during most of the year, but it can have very large flows during winter storms. The dam that forms Lake Henshaw is the only one on the river itself, but the river's drainage is extensively dammed. During the last 7 miles (11 km), the river flows through a 400-foot-wide (120 m) earthen channel with levees on each side to prevent flooding, although the rest of the river remains unchannelized. Urbanization, mining and agriculture have caused substantial deterioration of the watershed. Lake Henshaw, relatively close to the headwaters, is a source of drinking water. However, the water in the lower part of the river is only used for groundwater recharge. In 2009, a bridge was completed across the river near its mouth, replacing a small causeway that used to wash away every few years. Along the final 9 miles, the San Luis Rey River bike path follows it.
The San Luis Rey River rises in two main branches. The mainstem starts east of Rocky Mountain in the Cleveland National Forest and flows generally south-southwest. The West Fork's headwaters rise as a pair of tiny streams, Fry Creek and Iron Springs Creek, just to the north of Palomar Mountain. These two streams combine into the West Fork, which flows southeast through the Mendenhall Valley. The West Fork joins the main stem at Lake Henshaw, a reservoir formed by a dam across the main stem San Luis Rey River.
From the base of Henshaw Dam, the river winds west along the foot of the Palomars, followed by California State Route 76. It then bends southwest into a gorge. It leaves the canyon at the wide and spacious Pauma Valley, where it becomes a wash surrounded on both sides by agricultural fields. Potrero and Pauma Creeks enter from the right, then Frey Creek and Agua Tibia Creek as the river travels northwest. The river turns west, passing Pala, flowing through a patchwork of privately owned, government-owned and Native American lands. It then crosses under Interstate 15 and exits the foothills of the mountains near Bonsall.
After passing Bonsall the river flows generally southwest, through the cities of San Luis Rey and Oceanside. Although usually dry up to this point the river starts to contain water as it nears the mouth, both from seeps and from tidal activity that forms a lagoon at the mouth of the river. The San Luis Rey empties into the Pacific north of Oceanside, about 2 miles (3.2 km) south of the Santa Margarita River and ~30 miles (48 km) north of San Diego.
The first European land exploration of Alta California, the Spanish Portolà expedition, stopped at the river not far from the coast for two nights on its way north, July 18-19, 1769. On the return journey to San Diego, the party again camped near the river on January 22, 1770. Franciscan missionary Juan Crespi noted in his diary, "...we descended to a large and beautiful valley, so green that it seemed to us that it had been planted. We crossed it straight to the north and pitched camp near a large pool of water, one of several in the plain. At the extremities or ends of the plain there are two large villages."
The 2010 Rockstar Games release "Red Dead Redemption" features a river inspired by the San Luis Rey. The "San Luis River" serves as the border between the Western Border States and Mexico and is one of the hallmarks of the game.