The Arroyo Seco, meaning "dry stream" in Spanish, is a 24.9-mile-long (40.1 km)seasonal river, canyon, watershed, and cultural area in Los Angeles County, California. The area was explored by Gaspar de Portolā who named the stream Arroyo Seco as this canyon had the least water of any they had seen. During this exploration he met the Chief Hahamog-na (Hahamonga) of the Tongva Indians.
The watershed begins at Red Box Saddle in the Angeles National Forest near Mount Wilson in the San Gabriel Mountains. As it enters the urbanized area of the watershed, the Arroyo Seco stream flows between La Caņada Flintridge on the west and Altadena on the east.
The Arroyo Seco goes through Pasadena, where it passes the Rose Bowl Stadium as it goes through Brookside Park. The Arroyo Seco stream, which is fed by a watershed of 46.7 square miles (121.0 km2), helps to replenish the Raymond Basin, an aquifer underlying Pasadena that provides about half of the local water supply.
The Arroyo Seco then proceeds through the Los Angeles neighborhoods of Highland Park, Hermon, Montecito Heights, and Cypress Park. It ends at the confluence with the Los Angeles River near Elysian Park, north of Dodger Stadium and Downtown Los Angeles.