I had to go back and rethink the 1800 AGL foot thing. I had done that calculation using TOPO USA and figuring I my flight may take me directly over the river but it didn't. Looking at the video the trees directly below my flight path may have been pushing 400 AGL but that could be debatable. I would hate to admit to some violation I never actually committed. lol
The question I would like to pose to some of our in the seat pilots, Where can you fly in canyons and over tops of mountains? Do you need wingtip clearance or can you scrape the canyon walls on the way through? If I am at the top of El Capitan, launch from the top can I expect occupied aircraft to fly within 200 or 300 feet of a vertical cliff? How far out from a cliff can I feel safe I will not encounter a sight seeing group of airplane riders and pilot? I am sometimes concerned when I take off at 12,000 and go up 400 feet AGL, How much clearance do flyboys keep above a 12,000 foot summit?
Maybe @Gantech or @SportPilotAviation could help.
Lots of "variables" in those questions above. Technically going over anything *summit, hilltop etc* the aircraft would maintain required minimums (500', 1000' or whatever their current restrictions allow). In theory the flight path is ever changing to compensate for the varied terrain IF the pilot is "scud running" or trying to fly at the very min allowed flight. To make flight easier and a whole lot safer many GA pilots will find the tallest item on the sectional chart and maintain MIN clearance above that item. That way you're always "in the good". Also keep in mind that the altimeter on the aircraft is only as accurate as the settings dialed into the device. It's not an exact science unless you know some other "local" details and set the altimeter accordingly.
To further muddy the water it depends on what the operation of the aircraft is. MediVac, Forrest Fire etc would have very different operating altitudes than a fly through scenic flight.
Also in regards to "wing clearance" that depends on the pilot. Most will error on the side of safety and not get down into a situation like that but some are braver than others and are willing to sneak in low and close. I'm not sure what the regs are for "Canyon wall clearance" but I would imagine it's something similar to other clearance with a min being preset (500', 100' 1 mile etc) I just don't know what it is.