Lewis Pass (2,836 ft) lies on the main divide at the southern end of the Spenser Mountains, and is named after Henry Lewis (surveyor) who discovered it in the early 1860s. It is drained by the Maruia River to the east and the Lewis River to the west. The country is less steep and more open than that at either Haast or Arthur's Pass, and as a result this route is being developed as the main one for road traffic to the West Coast. Because of the high rainfall (over 140 in.), both sides of the pass support dense forest. During the last ice age the valleys on either side of the pass were occupied by glaciers whose effect was to steepen the sides of the valleys and to leave deposits of moraine and outwash gravel that can be seen in some road cuttings. To the north-east of the top of the pass, just out of sight of the road, is a small lake which has formed in a deposit of moraine left by a glacier that formerly flowed down the valley in which Cannibal Gorge has subsequently been cut. About 5 miles to the west of the pass, hot springs (Maruia Springs) occur along a fault zone; water from these springs (temp. 140°F) is piped across the Maruia River to swimming baths at the Maruia Springs Hotel.
by Henry Stephen Gair, M.SC., New Zealand Geological Survey, Christchurch.