The principal rivers west of the Main Divide of the Rockies are the Clark Fork of the Columbia and its principal tributary, the Flathead, which rises in British Columbia.
There is, however, only one large lake in the state - Flathead (or Selish) Lake, which may be regarded as an enlargement of Flathead river; it is 27 m.
The climate is generally dry, although less so on the mountains and in the Flathead river basin than on the Great Plains, and is subject to sudden changes and to great extremes of temperature; but the temperature varies more than the amount of precipitation.
The rainfall is sufficient for good grazing, but except in the Flathead valley cultivation was long considered to be dependent on irrigation; and consequently farming was only incidental to stock raising and mining until after 1870, and as late as 1900 the ratio of improved farm land to the total land area was less than in any other state or territory except New Mexico, Wyoming, Arizona and Hawaii.
The counties where dry farming had been carried on on the largest scale were Missoula, Ravalli, Flathead, Cascade, Fergus and Gallatin, where cereal yields, though not nearly so large as from irrigated lands, were high compared with the average for the country.
Cabinet (1,020,960 acres), Custer (590,720 acres), Deerlodge (I, 080,220 acres), Flathead (2,092,785 acres), Gallatin (907,160 acres), Helena (930,180 acres), Jefferson (1, 2 55,3 20 acres), Kootenai (1,661,260 acres), Lewis and Clark (844,136 acres), Lolo (1,211,680 acres), Madison (1,102,860 acres), Missoula (1,237,509 acres) and Sioux (145,253 acres in Montana; 104,400 acres in SouthDakota).
The Indians are mostly members of the following tribes: the Piegan, the Crow, the Salish (or Flathead), the Sioux, the Assiniboin, the Arapaho Atsina (miscalled Grosventres) and the Northern Cheyenne.
The Piegans, with small remnants of a few other tribes, numbering (1900) about 2060, occupy the Blackfeet reservation in the north-west of Teton county, the Crows, numbering 1857, occupy the Crow reservation in the south central part of the state; the Salish, with small remnants of the Pend Oreille, the Spokan, the Lower Kalispell and the Kutenai, numbering 1837, occupy the Flathead reservation in the north of Missoula and the south of Flathead county; Assiniboins and others of Sioux stock, numbering about 1793, occupy Fort Peck reservation in the south-east of Valley county: Atsina and Assiniboins, numbering about 1429, occupy Fort Belknap reservation in the east of Chouteau county; and the Northern Cheyennes, numbering about 1357, occupy Northern Cheyenne reservation in the south-east of Rosebud county.
Other fish native to the waters of the state are the sturgeon, catfish, perch (locally called pike), buffalo fish, flathead and sucker.