Have you checked with the game wardens on Pendleton itself about hunting there? They have very good deer hunting, and I have seen plenty of coyotes there. Just not sure if they allow you to shoot the yotes too.
Also, look out for the buffalo, and don't even think about shooting one. Fun to watch though.
If you cannot find a place on base, get a map of the Cleveland National Forest. Closest access for you would probably be out Route 76 to Palomar mountain. It's probably a 45-60 minute drive until you hit public land there.
Let me know if you have any other qeustions. I know a couple of the base wardens, so I could try to find out about yotes on base.
What does "gauge" mean anyway? As used here gauge means the number of round lead balls the same diameter as the inside of the barrel (aka the bore) that it would take to weigh one pound. It takes 12 lead balls the same diameter as a 12 gauge barrel to weigh a pound. The smaller 20 gauge would require 20 balls of that barrel diameter. The larger bore 12 gauge would require 12 lead balls of the bore diameter to weigh one pound.
In general the number of pellets in a shotgun shell...