okay, I think I found one via foot...is this one of those small practice tracks?
I even saw what looked like dirt bike tire tracks...which couldn't have been more than a week or two old.
but it has 2 bermed s-turns looping to a short straight and 3 "whoops" with a jump about 1' high. It's bordered by the freeway, so hopefully anyone riding it wouldn't be bothering anyone. The only problem is that snobby-looking cyclists go near there, who very likely would contact the authorities. And I don't know where else a rider could exit if the police came...and a hobo lives under the bridge nearby
I also found this single jump/berm, but it was better suited for a bmx bike:
and this was a single jump for a bmx bike, but relatively inaccessible for a motorcycle: