The Los Angeles River's official beginning is at the confluence of two channelized streams – Bell Creek and Arroyo Calabasas – in the Canoga Park section of the city of Los Angeles, just east of California State Route 27, at (the east side of Canoga Park High School). Bell Creek flows east from the Simi Hills, and Arroyo Calabasas flows north from the Santa Monica Mountains. From there the river flows east through a concrete flood control channel and very soon receives Browns Canyon Wash, which flows south from the Santa Susana Mountains. The river then bends slightly south and receives Aliso Canyon Wash, whose watershed adjoins that of Browns Canyon. The river then flows through the district of Winnetka, then Reseda and enters the Sepulveda Basin, a flood-control reservoir formed by the Sepulveda Dam.