Geological Survey Professional Paper 294—K The Rocks and Fossils of Glacier National Park: The Story of Their Origin and History

The mountains of Glacier National Park present an imposing front to the traveler from either east or west. On the east they rise with startling abruptness at the edge of the rolling, partly dissected lowlands of the western Great Plains. Monotonous plains topography gives way almost without warning to the diversified scenery of the Northern Rocky Mountains. The western boundary of the park is within that mountain unit, but it is marked by the relatively open valleys of branches of the Flathead River. The river flows into Flathead Lake in a great, nearly level trough known as Flathead Valley, which is thickly strewn with ranches, towns, and summer residences. From the Flathead Valley, the traveler approaches the mountains through the valley and over rounded, forested hills so that the cliffed mountains of the park burst into view suddenly.

The park contains parts of two of the ranges that constitute the Northern Rocky Mountains, a great assemblage that stretches from the eastern border of the park westward into the State of Washington. To avoid misunderstandings, one should remember that most Canadians and some geographers in this country give a less sweeping significance to the term "Rocky Mountains." Canadians commonly think of the western border of the Rockies as the series of major northwest-trending valleys, of which Flathead Valley in this country is a noble representative. These valleys are spoken of together as the Rocky Mountain Trench.

Plate 52 shows the names of the principal topographic features in northwestern Montana and adjacent parts of Canada. The mountain mass within Glacier National Park is made up of parts of the Lewis Range on the east and the Livingstone Range on the west. Although both names have been in use for a long time, the masses to which they should be applied remain in some doubt. Canadians call the part of the Livingstone Range that extends into Canada the Clarke (or Clark) Range and reserve the name "Livingstone" for mountains still farther north. In Glacier National Park the dividing line between the Livingstone and Lewis Ranges passes through Waterton Lake, up the valley south of that lake, over or around Flattop Mountain, down McDonald Creek, and through McDonald Lake to the Middle Fork of the Flathead. In present local usage, the Lewis Range constitutes the mountains within the park east of this line and stops at the southern boundary of the park. As originally defined over 50 years ago, the name was applied to the easternmost part of the Rocky Mountains almost as far south as Helena, the State capital. This usage still has much to commend it, even though part of the front range of the Rocky Mountains has since been called the Sawtooth Range by some people.

As plate 51 shows, the Continental Divide swings from the Livingstone Range to the Lewis Range at the north end of Flattop Mountain. The part of the park west of that divide is tributary to the Flathead River, whose water finally flows into the Pacific Ocean. Most of the park east of the divide drains into Canada through the Waterton, Belly, St. Mary, and Milk Rivers. All these rivers except the Milk River are tributary to Hudson Bay, at the northern border of the North American Continent. The Milk River and, farther south, Two Medicine Creek are tributaries of the Missouri River, whose water empties into the Mississippi and thence into the Gulf of Mexico. The fact that water that drains from the mountains of the park ends in such widely separated marine basins is marked by the name of Triple Divide Peak, which is about 6 miles south of St. Mary Lake.