That was incredible by it's own right but it also brings back so many memories!
Cajon Pass is part of my old stomping grounds, during High School I lived in Hesperia (way back to the left and behind the camera) up in the high desert where the pass leads to... I went to college at Cal State San Bernardino which is the other direction, beyond that huge wall of smog on the other side of the valley.
Later when I was living in San Bernardino a friend and I started flying slope gliders but to our knowledge there was never anything going on at Cajon Summit, but then again we flew them from Little Mountain in San Berdoo.
Here's my old plane, I went through a couple of these:
And here's little mountain, we flew off the slope to the camera's right, off to the side of the radio towers on the adjoining ridge:
I spent a LOT of time going up and down the two roads at the bottom of the valley in your video, which is the 15 freeway where it splits the northbound and southbound lanes going up to the desert. I lived in the dorms at Cal State and worked up in Hesperia on the weekends at a polishing shop, so every Thursday night it was drive up the pass, work Friday/Saturday/Sunday and go drink beer Sunday night before driving back down the pass.
Have some great memories of flying slope gliders. On very windy days with active Santa Ana winds it was crazy...had to duct-tape rocks to the fuselage of our gliders to have enough ballast to penetrate into the wind. Buckled the wing on my first Super Cheetah by diving then pulling up into a loop during what had to be 80MPH head-on winds. Other days you'd have the perfect amount of wind for a nice relaxing flight and we eventually got a decent group of regulars who would gather after work when the wind conditions were right, to share a 12-pack of beer or ummm, whatever, and kick back to cruise the slopes hunting for max lift while watching the sun go down. Awesome times.
The San Bdno. Sheriff's dept had an OH-6 or MD-500 that decided to have some fun with us one day, he came along and right in front of our launch area he pulled the nose up almost vertical and kicked the rudder over to execute a perfect stall turn. Right there at eye level with us...incredible!
One other time we were visited by a California Condor who showed up from behind, way up, riding the residual lift still coming over the hill above & behind us. I was flying and my buddy had landed his plane and when he said there was a Condor above us I didn't believe him but then looked up and HOLY FREAKIN' COW that thing was huge, unmistakable, with the white feather-stripes halfway out on the bottom of it's wings. They were rumored to be on the comeback and I'd only seen the two that they had at the San Diego zoo, but it was a Condor allright, I kid you not!
And my buddy had his glider bounced by a hawk one day, that just decided he'd had enough competition from these ugly flying things disturbing his efforts to find dinner.
After moving East my buddy got into paragliding and had an accident at Torrey Pines with a collapsed sport-class chute. Fortunately he eventually recovered and flies them again today. Meanwhile in Virginia, the "mountains" here hardly qualify as what would pass for hills back in California and we don't get much wind...if we do it's over property that someone (or the gov't) owns and doesn't want you on.
I really don't think you could ever find another form of R/C flying that is as pure, and would be as rewarding, than slope gliding...not to mention how accessible and easy it is to get into. You're fortunate to live in an area that makes it possible!