Follow the ledge along the right side of the dark, metal structure.
Take a running jump to the narrow, uneven ledge on the other side of the gap. Follow this ledge to the end...
...and kill a rattlesnake resting in the shade of a bush. Then take a running jump from the spot where the snake died, across the next wide gap to the ledge beyond. Continue around to the left, jumping over another small gap on the way.
When you reach the end of the last ledge, jump onto the sloping wall, slide back, and grab the edge.
Traverse to the left a bit and drop down onto the flat ledge below.
Follow this ledge to the end and around the corner to find a large medi pack.
To get back to the high ledge with the metal structure, face out across the canyon and climb back onto the previous ledge, which is now on your left.
Back up to the wall and then take a running jump across the quicksand to grab the left side of the rock outcropping. Pull up and climb to the top of the rocks.
Kill another snake and continue forward along the right side of the rocks to the top of the metal structure. Drop through the opening on top into the flooded tunnel below.