The area known as Devil’s Gate in the Arroyo got its moniker from a rock formation that, to some, reminded them of the Devil, complete with horns. Don’t bother to look for it know – time and the construction of the dam have all but obliterated it from the landscape. The Hahamongna watershed to the north was once a lake that was created by a natural dam that once existed where the Devil’s Gate is now. One day – for reasons unknown – the dam burst, eroding the rock and sediments that formed the natural dam, and created the natural formations somewhat visible today. The rapids that once traveled through this narrow point of the Arroyo are said to have made a laughing sound which, according to Tongva legend, was made by the river spirit and a coyote. Thus, this site may be the origin of the Hahamongna name. The first Los Angeles County Flood Control dam was built here in 1920 after a series of devastating floods in 1914 & 1916. Again, a lake formed behind the dam, but it soon silted up and became what is today the Hahamongna Watershed Park.