We’ll see if this turns into something or not. Total speculation on my part but here’s what I think happened:
Gun owners in LA and Orange counties don’t have a lot of areas to go shooting. You either join a local club or you take a 1 1/2 to 2 hour drive out of the LA basin and into the Mojave desert to go shooting.
So these guys headed up the I-15 and probably stopped at the first area they saw was somewhat barren. Not having local knowledge they did not know this area is crawling with hikers and campers and started blasting.
Out here it’s not uncommon to see large groups of people shooting in what seems like an unorganized manner. San Bernardino is as gun-friendly as you get in California. So what you have is a bunch of dumb out-of-town gun owners who didn’t bother to research the regulations about shooting locations in San Bernardino County and scared the locals.