new zealand co-operative dairy company started mining at glen afton in 1921. the 2.5 km extension from rotowaro to pukemiro and glen afton was built between 1915 and 1924, although a further proposed extension beyond glen afton did not proceed. the hill section from rotowaro to glen afton was difficult to construct, with a large "summit" cutting just before glen afton. grades on the hill section were up to 1 in 50, with 150m (7.5 chain) radius curves. at the same time as the extension, tablet signalling was introduced between huntly and glen afton.