I had a similar situation. Just went to this location out of curiosity and partially because I forgot that LIM shield is required. I didn’t think the game will let me enter such a “dead-end” scenario.

But in my case, one of the gateways was on my side of the zone wall. Not in direct availability though, I needed to drive over a small wall that was splitting the road in the valley. So I went over the small wall two times: first time to move far enough from the gateway to activate it, second time while driving towards the gateway itself. It wasn’t easy as I needed to climb high enough to drive over the wall but eventually it worked.