Two Thumb Range

An eastern spur of the Southern Alps, the Two Thumb Range runs in a predominantly north–south direction for approximately 45 kilometres (28 mi). It and the smaller, mostly parallel, Sibbald Range branch from the Southern Alps close to Mount D'Archaic, 40 kilometres (25 mi) northeast of Aoraki / Mount Cook. The two ranges are separated by the valley of the Macauley River and form a barrier between the valleys of the Godley River and Lake Tekapo to the west and the Rangitata River to the east. Much of the eastern side of Lake Tekapo is separated from the range by the lower Richmond Range branch. As for the Richmond Range branch of the range, several smaller ranges branch off towards the east including the Black Mountain Range from near Achilles Low Peak, and the Brabazon Range from Mount Caton. The Two Thumb Range's peaks diminish in size towards its southern end, which is immediately to the east of the town of Lake Tekapo, after which it splits into two less significant ranges, the Rollesby and Albury ranges. At the saddle between the Two Thumb Range and these ranges, State Highway 8 crosses Burkes Pass on its route between Lake Tekapo and Fairlie.^[5]

The South Opuha, Havelock, and Coal Rivers have their sources within the Two Thumb Range, as do numerous smaller watercourses, the most notable of which is Forest Creek, a tributary of the Rangitata River.

The Thumbs twin peaks in the range have been described as "twin peaks like two giant thumbs … a famous mid-Canterbury landmark."^[2] The names of several of the range's peaks, including Achilles Peak, Exeter, and Graf Spee, commemorate New Zealand's involvement in the Battle of the River Plate. There may be potential confusion over the names as for example Achilles Peak is the official name,^[12] for the highest peak of Achilles, where Achilles is an unofficial name, located as the saddle between two peaks,^[11] that are called High and Low peaks. Further there is a Mount Achilles in Otago.^[11] Mount D'Archiac was named by Julius von Haast after the Adolphe d'Archiac.^[1]

Torlesse Composite Terrane rocks form the basement and range in age from the Jurassic near the Southern Alps to Permian in the east.^[41]: 141 Most of the Two Thumb Range consists of unfoliated metagreywackes, with areas of pumpellyite-actinolite.^[41]: 1412

There is current and Quaternary displacement east of the Alpine Fault that has been ongoing for less than 5 million years that has resulted in uplift of the Two Thumb Range.^[41]: 141 The northern range is uplifting as part of the Southern Alps while distinct faulting structures are known in the southern portion. To the east of the ranges are two series of north-striking Fox Peak faults and to the west the northeast-striking Forest Creek faults that parallel the Alpine Fault at about the Mount Musgrave level in the southern range.^{[41]: 144–7} A fault is inferred to separate the Round Hill area from the rest of the ranges.^[41]: 148 It has been postulated that the southern Two Thumb Range has uplifted about 2 km (1.2 mi) in the last 1.5 to 2 million years.^[41]: 150

Dobson Peak and its surrounding terrain are the home of the Mount Dobson skifield.^[42] The smaller Roundhill Ski Area is also located within the range.

New Zealand's major north-to-south walking track, Te Araroa Trail, crosses the Rangitata River before following the valley of a tributary, Bush Stream, into the Two Thumb Range. It crosses the range at Stag Saddle — the trail's highest point at 1,925 metres (6,316 ft) — immediately to the north of Mount Hope, before following the eastern shore of Lake Tekapo south.^[43]

The Two Thumb Range was the setting for Desmond Bagley's 1975 novel, The Snow Tiger.