All of waterworks could be in the cave, blocked off with a rock. Simmons did make the cave a BIG point in the Red Vs. Blue intro. Edit: Wow. I feel stupid. Sorry STFU. Just missed your post.
That area you pointed to connects to a cave towards the coastline, and possibly also a pathway up to alaska. This map I made shows the layout of Forge World fairly well. Check Halopedias article on Forge World for some decent pictures, or just look on B.net or YouTube for some veiws of the area you indicated. Click here. Im expecting some gameplay footage of Grifball or Paradiso because they are going to ship as variants on the disk, and so far we haven't seen anything from them really.
It's past the 22nd (For me) and there is nothing. So, Problably not true, or they are late, again, like their update...