A river runs through it sometimes: San Fernando Valley History

Old maps did not agree on the source and the path followed by the Los Angles River across the Valley. Before the 20th century, mapmakers often believed that the river originated in the San Gabriel Mountains and plunged southward over the Valley floor, since that is where the tormenting winter and spring floods began. Some maps also showed the river rising at Encino and gurgling eastward to the Narrows.

The confusion us due to the river's fickle flow. As understood now, the headwaters of the Los Angeles River rise in the Simi Hills, where Bell Creek gathers the runoff from springs and scant rainfall. The creek trickles out of the Bell Canyon and merges with Calabasas Creek to from the river-if the term can properly applied to a waterway of such dubious existence. Except in rainy season, most of the river's flow access the west valley underground. Maps likely showed the river appearing at Encino because, in dry months, the underground flow would first appear on the surface there.

Today the official starting point of the Los Angeles River is where the two concrete streams behind the bleachers of the Canoga Park High School football field. Go Hunters.

This information was plagiarised and taken from Kevin Roderick's awesome book: "The San Fernando Valley: America's Suburb." Check it out.