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 city of
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 south of the
Santa Margarita River and about north of
San Diego. ==Water resources==