Judging by other videos by the same pilot, it's Lake Elsinore in southern California. If you scroll through the comments, you see some other observations by the OP.
Here's my favourite:
Many interesting, funny and spooky stories came from this outlanding. One involved the very first vehicle to come down that deserted road. It was the garbage truck. The guy drove up, stared at my plane sitting atop the pile of garbage, looked me in the eyes, shrugged his sholders and drove off without another word.
I got caught in a similar situation once, but luckily in a high performance glider and was able to reach a notch in the ridge and fly through. It certainly raises the adrenaline level.
Full marks for posting the video