In the north the Rocky Mountains consist principally of two parallel ranges, the Lewis and Clark Range to the east, and the Livingston Range to the west, which were formed by a great overthrust; between them is the Waterton-McDonald valley, 8-15 m.
The Rio Grande and its principal tributary, the Pecos, drain narrow basins in the S.W.; these two rivers and the Canadian river rise in the Rocky Mountains in Colorado and New Mexico, but all the other rivers by which the state is drained rise within its borders.
Some, for instance, may consider that the chamois and the so-called white goat of the Rocky Mountains are entitled to be included in the group; but this is not the view held by the authors of the Book of Antelopes referred to below; and, as a matter of fact, the term is only a vague designation for a number of more or less distinct groups of hollow-horned ruminants which do not come under the designation of cattle, sheep or goats; and in reality there ought to be a distinct English groupname for each subfamily into which "antelopes" are subdivided.
East of the Cascade Mountains the Columbia and Spokane rivers mark the boundary between the Okanogan Highlands to the northward and the Columbia plateau to the southward; The Okanogan Highlands, an outlier of the Rocky Mountains extending westward from the Coeur d'Alene Mountains in Idaho, reach heights of 5000 to 6000 ft.
The main range of the Rocky Mountains separates that part which is drained west into the'Columbia river and the Pacific Ocean from that which is drained east into the Missouri and Mississippi rivers and the Gulf of Mexico, and from a very small part which is drained north-east into Hudson Bay; the water-parting which in Montana separates the drainage into Hudson Bay from the drainage into the Gulf of Mexico crosses only the north-west region of Teton county.
