Lake Hodges Dam is a multiple-arch dam that sits on the San Dieguito River. It was commissioned by the Volcan Water Company and designed by John S. Eastwood. It was completed in 1918, and later purchased by the city of San Diego. Water from the Lake Hodges Reservoir services the customers of the Santa Fe Irrigation District and the San Dieguito Water District.
Personal Experience: I am putting this spot up here for historical reference, and not encouraging people to actually explore it. This spot is very dangerous and serious injury or death could occur. This is also a private property area and trespassing is strictly prohibited. With that said, I will let the photos speak for themselves.
Near the flume we found some old ruins and a tunnel:
The top is super-high!