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 May, 1914 BIRDS O1 NORTHltRN MONTANA 125 ern part of the state, due to the fact that along the northern border the eastern prairie region extends farther westward than elsewhere, and in fact reaches the eastern base of the mountains forming the continental divide. ! have in- eluded with Teton County that portion of Lewis and Clark County that lies in the drainage of the Sun River (see fig. 39). The southern boundary of Teton County is formed by the North Fork of the Sun River, but since my ob- servations covered both sides of the river, and the character of the country is essentially the same on both sides, I have made the divide between the drain- ages of the Sun and Dearborn rivers the southern boundary of the region stu- died. This divide forms a natural division between different regions of the state, the character of the country being markedly different on the two sides of it. In studying the distribution and occurrence of the birds of this region, it may lie c)nsidered in two main parts, the prairies and the mountains. The Fig. 39. VEW IN THE CANADIA.- ZOlE ON THE SUN- RIVER, LEVlS AXD CLARK COUNTY, MONTANA. prairies occupy the eastern portion, and cover considerably more than half of the total area. They lie entirely within the Transition zone, and their altitude varies from 3500 to 4500 feet. They consist of open grass land, rolling hills and flat-topped benches, steep-sided buttes, and broad valleys, watered by streams that are bordered by cottonwood groves and willow thickets. Alka- line ponds and lakes are quite frequent, in fact very numerous toward the westward, along the edge of the lower mountain slopes. The mountains occupy a comparatively narrow strip through the western part of the counties. They embrace the headwaters of-the Sun, Teton and Two Medicine rivers, and Birch Creek (see fig. 40). They lie in the Transition, Canadian, Hudsonian and Alpine zones, and range from 4,000 to 9,500 feet in altitude. These mountains are extremely rough, consisting of numerous liee- stone ridges with precipitous sides. In many places most of the timber has