On the way to Coral, go to the switch that you push to let the others go through. If you explore around that area, you should hear birds chirping. Go up the hill where you hear it (you might have to search to find the right spot) and pick the first choice you are given.
After collecting the 10 Phoenix Downs, go back down to the lower tracks and follow your partners. As they turn to the right, you need to take the left split because buried in the hill under the tracks is a cave with an out-of-work miner. A Power Source, Mind Source, and Tent may be acquired within this hidden area.