It’s just water canyon rd all the way from Cubero to the WMA. It never crosses into Rez unless you turn off one of the side roads and you don’t really climb any hills either. Not sure if there’s a back way into it I’ve never taken or you’re thinking of Marquez.
You don’t actually go through any Rez to get to water canyon. You travel through the Cubero land grant and as long as you have any valid tag you can go hunt that WMA.