As it's a test flight I might suggest it is Lake Elsinore, California.
Just a thought
And a good thought, at that ! Yes, it's at Lake Elsinore, where Northrop first flew the N3PBs.
merlinxx, Hennessey's must be in Avalon then, eh? I usually made it no further than the airport at the NW end of the island.
Cheers,
Tom