This auto ramp leads down to a dual-purpose underground garage and large bomb shelter at Frenchman Flat. The Federal Civil Defense Administration
facility was designed by Ammann & Whitney Consulting Engineers in 1957.
The underground garage is still in place today. The "Priscilla" nuclear weapons civil effects test subjected the garage to 30-pounds per-square-inch
of overpressure.
Not really secret, but cool I thought if you're into underground stuff.