The San Fernando Valley, a 10 mile by 20 mile rectangle at the Northwest corner of Los Angeles, CA, was once a lake fed by four rivers (now creeks). From the West, Calabasas creek and from the Northwest, Chatsworth/Bell creek converge in Van Nuys, by Bull creek from the North then, in North Hollywood, by Tujunga creek from the Northeast. The River then leaves the Valley, ocean-bound.

The Japanese Garden site is located at the junction of the River and Bull creek, almost in the direct center of the Valley. The site is behind the Sepulveda Dam in the Sepulveda Flood Control basin which could impound 17,300 acre feet of water in about 2.25 square miles. The dam is earthen, 57 feet high, and located at the Northwest corner of the San Diego and Ventura Freeways. The basin is roughly bounded by Balboa and Victory Blvds.