Where does the water come?

Rain

The water does not come from the Rockies. The Rockies are in Colorado. From Wikipedia: Cull Canyon Regional Recreation Area (CCRRA) includes a fishing lake and a separate 1.5 acres swim lagoon that resulted from damming San Lorenzo Creek. I've included a map of the creeks and watersheds of the East Bay. http://explore.museumca.org/creeks/MapOak.html

of the rocky mountains