1. Go down to the cave. Open the gate. When you are locked in, use the axe to loose the rocks. Squeeze through the crack in the Rocks and continue to follow the way out to the "big drop".
2. Investigate the area and find Brian Goodwin's camp. There is a "Bundle of Pitons" on the table. Take it. Now you can use the pitons to climb down those black cracks in rocks. Use one of the Pitons on one of those cracks near the camp. Now you can climb down and hike back to the cave. You need to open the gate again.
3. In the cave, when you turn left, there is a cracked rock you can use. Do it and climb down. Follow the cave down and you'll find the body of Brian Goodwin. Climb over him, get to the surface. As soon as you're out, you can report the body.