When Haast arrived in Canterbury to begin his survey of their portion of the West Coast, the Superintendent of Canterbury William Moorhouse instead requested that he investigate the mountain range between Lyttelton and Christchurch. A rail tunnel was proposed through the mountain to link Lyttelton and Christchurch but engineers had encountered particular tough basaltic rocks which jeopardised the proposed route. As a result of Haast's work, the rail link was able to proceed. He became provincial geologist to Canterbury, a post which he held from 1861 to 1868.