This ramp exists, or once existed, somewhere in the LA area:
I don't know anything more about it than what you see in the 2012 picture above. I did once skate with Tom Schaar at the combi bowl when he was 12 years old and not yet famous, and we talked a few times. I told him if he could land that 720 he was trying, it would be the first one I've ever seen in real life... and sure enough he stuck it.