Black Rock Quarry Restricted Area. The way I entered this area was by dropping down this elevator. Use Levitate to climb the platforms and then follow the sewers until you find a door that leads you back to the Furnace Chamber.
In the Black Rock Quarry Entrance where the Astral monster is is a door in an above alcove you can enter. You will get here when looking for the Janitor. Find a Black Rock Prism.
Basically its high up in the south of the quarry.
Find the Black Rock Quarry in Control. Mixed glass paper cardboard cans plastic cartons textiles shoes Additional information. Walk along the top of the quarry and use your levitation when needed to reach the open hangar doors on the northside. The quest I just finished in this area was.