Haha, you're deep down the rabbit hole now, my friend. Your guess looks a lot better than the previous location, for sure. Turns out that NID has a pretty decent website, and they mark it within the park, but a little further north: https://nid.sec.usace.army.mil/#/dams/system/CA01079/description

BTW, nice work on that Beverly Johnson "park" along Whitnall - I ride past it fairly often and never knew it had a dedication/name.