The chief surveyor, Thomas Cass, commissioned Arthur Dobson in 1864 to find out whether there is a suitable pass from the Waimakariri watershed to the West Coast. George and Arthur Dobson set out in March 1864, later to be joined by their brother Edward at Craigieburn. While George surveyed road lines there, Edward and Arthur proceeded to explore the high country. On the advice of West Coast Māori chief Tarapuhi, they found a pass that steeply descended to what became known as Otira; the route had long been used by Māori for trading pounamu. Arthur prepared a report, which included a sketch of the unnamed pass, and presented it to Cass.