I was gonna suggest The Jacumba Exit gas stations as a good meeting spot due to familiarity and the gas.
As for ranges, the Rez dump is kinda small. 4-5 cars at the loop at most will fit.
The small range (#2 in the pics)is at the end of an off-road vehicle area, so there is a ton of room there. It is an old abandoned range, so no rules or RSOs there. And if any of you are into R/C aircraft, you have to drive right by an R/C aircraft field out there, so you can geek out on that. Those old-timers out thare are pretty serious.
Adair is a range, but I have never seen an RSO or any range personnel out there. Last time I shot there, it was with my Ordnance shop from MCAS Yuma. We had a cooler full of beer out there. I don't plan on drinking and shooting, mind you, just trying to give you an idea of how relaxed it was when I was there.
It has plenty of room, and a 1,000 yard range. It is worth checking out at least. Fortunately all the areas are fairly close together. Oddly enough, Adair also has an R/C field.
I googled Sprague's, the main gun store in Yuma and found this:
http://www.spragues.com/wheretoshoot.html
Really good info.