The river officially begins at the confluence of two streams, Santa Ysabel Creek and Santa Maria Creek, near the town of San Pasqual. Santa Ysabel Creek rises in the northeastern corner of the San Dieguito River watershed and flows west, creating Lake Sutherland. It then flows out of the lake's dam and westwards for the rest of its course. Its total length is about. Santa Maria Creek, the smaller of the two streams, begins near the city ofRamona and flows northwards about through the Ramona Grasslands and Bandy Canyon. A third fork, Temescal Creek, rises in the Cleveland National Forest near Lake Henshaw and flows south about into Santa Ysabel Creek. From there the river flows west past the city of Escondido, and under Interstate 15 before being impounded by the Lake Hodges Dam to form Lake Hodges. From the dam to its mouth, the river flows through the long and narrow San Dieguito River Park past Del Mar, and broadens into a tidal waterway and a lagoon as it crosses under Interstate 5 and past the Del Mar Fairgounds to empty into the Pacific Ocean at Del Mar, California.
Watershed
The San Dieguito River watershed has vast areas, over 83%, of open space. As a result, it provides habitat for hundreds of plant and animal species. Vegetation cover ranges from pine forest on the slopes of the headwater mountains to arid grassland on the plateaus and plains further downstream. However, 18% of the basin, mostly along the shoreline, is devoted to urban areas. About 150,000 people live in the San Dieguito River watershed, but could expand to 210,000 by 2015. The lower river suffers from pollutants that affect rivers all over Southern California, mainly from E. coli bacteria from urban runoff.
History
Prehistorically, the San Dieguito tribe inhabited much of San Diego County, with their main villages on the San Dieguito River. Remains of this culture are identified as the "San Dieguito River Complex". By the 16th century, most of the basin formed the southern part of the Luiseño tribal territory. The Portola expedition of 1769 camped at the river, not far from the coast. On the De Anza Expedition's way back to Mexico from San Francisco Bay, Father Pedro Font mentions "San Dieguillo" in his diary on January 10, 1776. An Indian rancheria, San Dieguito, is mentioned under the jurisdiction of the San Diego Mission in 1778. In 1840 or 1841, after the Mission Period, the name was applied to the Rancho San Dieguito, which was granted in 1845. The rancho name was later changed to Rancho Santa Fe.
