Was doing some exploring last night, and figured I'd check out the "secret cave" in The Black Garden story mission. Neat stuff.
But upon checking every corner, I worked my way back to the entrance that had been closed up behind me.
After poking around for a bit, I found my way outside of the cave, and standing over a NEW secret area.
A heavily glitched out-of-bounds Tharsis Junction! Ohhh, so THAT'S why the cave reads as Tharsis Junction.
Enjoy!
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There's another way to get there. Much easier, lol. It's how you get into the black garden on patrol.