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!