The Columbia Mountains rise from the plateaus of the Central Interior and extend eastward to the Rocky Mountain Trench. Geologically distinct from the nearby Rockies, the range is divided into four sub-ranges: the Cariboos, Monashees, Selkirks, and the Purcells. Glacier encompasses a portion of the northern Selkirks and a narrow strip of the northern Purcells. The topography of the park varies between rounded mountains and ridges in the east, north, and west, and sharp, steep-sided peaks in the central and southern regions. A.O. Wheeler measured many of the park's mountains in 1901 and 1902 using a complex system of fixed points and photographs. In the early 20th century, the area was referred to as the Canadian Alps. Most names are from historical figures, including explorers, surveyors, mountaineers, and railway and Hudson's Bay Company executives.