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 Portolà, who named the stream Arroyo Seco because its canyon had the least water of any he had seen. During this exploration, he met the Chief Hahamog-na (Hahamongna) of the Tongva Indians.