Should be somewhere around the cliffs, where I painted it red.
I dropped into it 2 times (yeah, I am that dumb) while standing on that mountain firing on the enemy team that was camping in their own base.
I walked backwards, down the hill, to avoid being blown to pieces, and suddenly im in a hole, just big enough for my Bushy to turn around, but too steep to walk out of it.
EDIT:
Found it

That hole is too steep to be exited by anything without JJS, or at least to be left by Bushwackers.
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