I should have grabbed screenshots when I was there, but on the west side of Westfall there is a camp of level 13 defias with like a windmill or something there, which will constantly respawn if you kill them all. You'd need AOE to make the most of it though.

Then in the cave also on the west side, there are constantly some level 15 gnolls or defias mobs spawned. They're not quite as grouped up though so you have to run through the cave and keep killing them.

Is it the crabs/crawlers that respawn constantly on the beach? I'll have to check that one out.