My impression was they were at the top of the cliffs, not the bottom.
Those cliffs are near vertical, so back of valley or top on Kokee are almost same thing. A typical tour route, (I have flown this route thousands of times), would have you cross the front of the valley then right turn towards the back wall and do a left descending turn in the valley and come out the front. So pure guess work, he may have hit the back wall, but pure speculation at this point.