Talk to Delilah to update your objective, and then follow the wave receiver all the way back to the place where you fell on Day One. Use a rope to rappel to the bottom, and follow the trail West, then down the first Northward trail you can. Your wave receiver will lead you to a collar, a cassette tape, and an arrow pointing up with your name. Climb to the top, and follow the path all the way to the end. Explore.
Your objective will update, so head North to Thoroughfare Lookout. Keep going until you get to the cable car, and take the ride. Head to Delilah's tower, and pickup the radio headset. After you're done, exit the tower, and walk towards the helicopter.