Geography & Geology

Rapids in Swan River as it enters Flathead LakeThis 1846  map drawn by Jesuit priest, Father Peter John De Smet, is perhaps the earliest published depiction of the geography and water courses of the Flathead region.

In 1840 Father De Smet left St. Louis Missouri, charged with bringing the Catholic faith to the native tribes of the Northern rockies.  For the next six years he worked to establish missions for the Flatheads, Pend Orielles, and Blackfeet and greatly influenced their acceptance of Christian theology.

Returning to St. Louis in 1846 De Smet published several popular books on Indian life and continued his efforts to financially support the Indian missions of the Rockies.

Although De Smet visited the Flathead, this map was based on information obtained from the native inhabitants of the area.  The Kootenai referred to Swan Lake as “Nasoquat”, but De Smet gave it the name of “Lac Hughes”, in honor of Arch bishop John Hughes.

THE SWAN VALLEY – GEOGRAPHY AND GEOLOGY De Smet1846 Map

The Swan Valley is located in northwest Montana, roughly at latitude 47° 33” N; longitude 113° 45” W. It is west of the Continental Divide and thus enjoys a Pacific Northwest type of climate, with more moisture and moderate temperatures than eastern Montana. The Swan Valley is about 93 miles long and drains an area of roughly 671 square miles. The valley is bounded by the Swan Mountain Range to the east and the Mission Mountain Range to the west. The Swan Range rises abruptly from the valley floor of about 3,000 feet to peaks above 9,000 feet high – often within 10 horizontal miles of the river.[1]

These two mountain ranges both extend south beyond the headwaters of the Swan River (which flows northerly into Flathead Lake at Bigfork) to the Clearwater River drainage, which flows southerly to join the Blackfoot and Clark Fork rivers. A low divide at about 4,200 feet separates these two river basins, and the combined drainages are referred to as the “Seeley -Swan” Valley.

Both the Swan and Mission ranges are Precambrian sedimentary formations, created by long faults or lines of surface movement. An up-thrust block fault scarp forms the steeply rising Swan Range to the east. Both ranges have formations tilting down to the east. Related to the sedimentary foundation, no significant mineral deposits have been found in the Swan Valley.[2]

The Swan Valley was probably affected by several glaciers during the ice ages, resulting in “U” shaped canyons and an undulating valley floor with many small lakes and bogs. Geologists believe that one such ice sheet flowed south in the Rocky Mountain trench from the Yukon to the Flathead Valley, where it was split by the Mission Mountains, with one portion flowing down the Swan Valley. Nearly half of the Swan basin is now covered with glacial deposits.[3]

Annual precipitation in the valley ranges from 20-30 inches at lower elevations to 80 inches or more in the mountains. Average annual precipitation in this roughly 430,000 acre basin is about 1.5 million acre feet, or a basin average of 41 inches. Comparing this precipitation to the Montana state-wide average of 15 inches per year shows that the Swan Valley is unusually wet for our state. This relatively high precipitation and the above noted glacier-created bogs, basins, and lakes makes the Swan Valley truly unique, as the basin is a huge water reservoir. In fact, about 16 percent of the Swan basin surface is covered by some type of water – lakes, rivers, ponds, and bogs. This is the highest proportion of surface coverage of any river drainage in Montana, and represents a great natural resource of increasing value.

High precipitation with deep winter snows encouraged dense forests and discouraged both permanent villages by Native Americans and later settlement by Euro-Americans. The lack of mineral deposits further delayed development of the area relative to other locations in Montana. These all become important factors in the present environment of the Swan Valley and its history, which will be reviewed in other chapters. SOURCES/BIBLIOGRAPHY Curtis, Lori S., Flathead Watershed Sourcebook: A Guide to an Extraordinary Place, Flathead Community of Resource Educators, 2010 ——-, Swan Valley and Condon Community Profile, Swan Valley Community Council Sept 21, 2010 Whitehorse Associates, Source and Ecological Classification, Swan River Basin Montana, Fws.gov/Montana field office, Jan, 1996

[1] ——–, Swan Range, www.wikipedia.org

[2] Alt, David and Hyndman, Donald, Roadside Geology of Montana, Mountain Press Publishing, Missoula, MT, 1986

[3] Ibid