Along the ICE AGE FLOODS
NATIONAL GEOLOGIC TRAIL

Glacial Lake Missoula Strandlines Ice Age Floods National Geologic Trail Imagine you are standing on the edge of glacial Lake Missoula 15,000 years ago. You can hear lapping waves cutting benches known as “strand-lines” into the shoreline. Today, you can see these huge strand-lines on hills surrounding Missoula, Montana, marking changes in lake level over time. On Mount Sentinel, marked with an “M”, and Mount Jumbo, marked with an “L”, the strand-lines are seen as horizontal lines in the vegetation or highlighted by snow in the winter. Public hiking trails switchback through the strand-lines on Mount Sentinel and Mount Jumbo. Ancient shorelines or strand-lines of Glacial Lake Missoula are visible as perfectly parallel horizontal benches on hillside slopes around Missoula. They are most visible with light snow cover, or in low evening light on the mountains marked with an”M” and an “L” on either side of Hellgate Canyon looking east from the downtown.  These shoreline benches cut by wave action in the lake recorded various lake levels as the ice dam blocking the Clark Fork River far upstream on the Idaho border repeatedly failed and refilled 40 times or more.  It may be that as the ice-age waned each successive ice dam that reformed was smaller and failed under less pressure from a lower lake level than the one before, leaving behind its bench as a record of the successively lower ancient lake shorelines. It’s also possible they record winter still-stands in rising lake levels over time.  Quick Facts Location:The Kim Williams Trail at Van Buren and 5th Street leads from the U Montana campus along the river between the mountains. To reachhigh water markers on the mountains see the Interactive Map or go to GlacialLakeMissoula.org 

Glacial Lake Missoula National Natural Landmark Ice Age Floods National Geologic Trail Glacial Lake Missoula was the largest of several lakes impounded by the Cordilleran Ice Sheet in the Northern Rocky Mountains during the Quaternary period. The lake was approximately 2,900 square miles in size and contained more than 500 cubic miles of water. It occupied the Mission, Jocko and Little Bitterroot valleys, drained by the Flathead River; and the Missoula, Ninemile and Bitterroot valleys, drained by the Clark Fork River. The lake was formed by an ice dam across the mouth of the Clark Fork River at Lake Pend Oreille, Idaho, a result of successive advances of a lobe of the Cordilleran Ice Sheet. The site is located 12 miles north of Perma, Montana.At least three and possibly more than 100 separate collapses of the ice dam, possibly coincident with periods of ice retreat, caused the lake to drain, producing catastrophic floods across the Columbia Plateau and down the Columbia River Basin. It is estimated that the waters of Glacial Lake Missoula, 1,000 feet deep at Eddy Narrows, were withdrawn at a peak discharge rate of 10 cubic miles per hour. Approximately 550 cubic miles of water passed through those narrows during withdrawal. Evidence of this catastrophic withdrawal can be found in scourings, high eddy deposits of flood debris, flood bars of boulders and course gravel, and successions of giant arcuate ripples or ridges of gravel resting on bedrock surfaces. Ripples appear as ridges 15 to 50 feet high, 100 to 250 feet wide, and from 300 feet to a half-mile long. While the form, structure and arrangement of these features are similar to that of ordinary current ripple marks, they are termed giant flood ripples, due to their large size. The giant flood ripples at this site are unusual due to their being on the down-current side of notches in a ridge separating two basins that were both subsidiary to the main course of Lake Missoula in the Clark Fork Valley. The best examples of giant flood ripples are found in Camas Prairie. Quick Facts Designation:National Natural Landmark OPEN TO PUBLIC:Private Land, closed to the public, but features throughout the area are visible from many vantage points.

Travelers’ Rest State Park Ice Age Floods National Geologic Trail Located at an historic and contemporary crossroads, Travelers’ Rest State Park and National Historic Landmark is a place where visitors can say with certainty that they are walking in the footsteps of Lewis and Clark. The Park is at the core of a campsite used by the Corps of Discovery from September 9 – 11, 1805 and again from June 30 – July 3, 1806. In the summer of 2002, archaeologists uncovered evidence of the Corps of Discovery’s visit to the area, including a trench latrine tainted with mercury, fire hearths, and lead used in the repair and manufacture of firearms. The discovery makes Travelers’ Rest the only campsite on the Lewis and Clark Trail with physical evidence of the expedition. For centuries Native Americans also used the area as a campsite and trail junction. Salish, Pend d’Oreille and Nez Perce peoples were among those who traditionally occupied the area. Native American storytellers bring their history, culture and society to life as part of the programming at Travelers’ Rest State Park. The Bitterroot River is the primary body of water in this area, now running about 500 feet below the surface of what was once Glacial Lake Missoula, which extended all the way to the area now indicated by a high water marker at Lake Como.  There are few vestiges of the Lake in this area but information and a display are located at the Visitor Center. Travelers’ Rest is an idyllic spot for strolling the park’s trails, and offers a rich bird habitat, with more than 115 species recorded within the park boundaries. Quick Facts Location:Located 1/2 mile west of Lolo on Hwy 12 Significance:Located at the crossroads of culture, this is the only archaeologicaly verified campsite of the Lewis and Clark Expedition, as well as the traditional homeland of the Selis Qlispe people. Designation:National Historic Landmark