The expedition was initially based at Tingri to the north of Everest from where the northern and western approaches were explored. While the surveyors and climbers carried out this work, the leader of the expedition, Charles Howard-Bury headed back east to find a suitable base for exploration from the east of the mountain. Knowing by this time that the North Col was a likely good route, Howard-Bury found the glacial Kharta Chu which he guessed might originate from the North Col. He returned to Tingri and then the whole expedition moved to Kharta. From there various parties explored the Kharta and Kama valleys (see maps) eventually discovering that the Kama Chu came from the unscalable Kangshung Face. It turned out that the Kharta Chu came not from the North Col but from the Lhakpa La. Reaching this col they found that the only way from there to the North Col was to descend some 1200 feet to the upper East Rongbuk Glacier and climb back up to the North Col. This climb was achieved by George Mallory, Guy Bullock and Oliver Wheeler on 24 September 1921 but they could get no further and had an arduous return.