On the same expedition, Oliver Wheeler first explored the East Rongbuk Glacier. His exploration below the Lhakpa La pass led him on 3 August 1921 to realise that the East Rongbuk Valley provided the key to a viable route to the summit of Everest. A few weeks later, a party consisting of George Mallory, Guy Bullock, and Oliver Wheeler explored the head of the valley via the Lhakpa La pass to become the first people to reach the North Col of Everest and set foot on the slopes of that mountain. See .