Idaho State is known as the "Breakout Zone" for the story of the Ice Age Floods. The Ice Age Floods broke loose and helped form Lake Pend Oreille in northern Idaho. Glacial deposits and remnants of the Ice Age Floods litter the surrounding area. Many of the other lakes in the region owe there origin to Ice Age Floods deposits. Explore Idaho and learn more about how the Ice Age Floods impacted the region below.
12,000 to 17,000 years ago a 4000' tall ice dam blocked the path of the Clark Fork River creating glacial Lake Missoula. During the Ice Age Floods this ice dam failed, releaseing more water then is held in modern day Lake Ontario and Lake Erie combined. 600 cubic miles of water rushed through this area and down Lake Pend Oreille destin for the Pacific Ocrean.
View the Green Monarch Ridge and the Purcell Trench from a large pullout on Idaho State Route 200, about one mile (1.6 km) west of Hope, Idaho and 15 miles (24 km) east of Sandpoint, Idaho.
The Purcell Trench Ice Lobe originated in Canada and flowed south into Idaho, guided by the structural control of the Purcell Trench. Following the path of least resistance into the basin now occupied by Lake Pend Oreille, it was impeded by the Green Monarch Ridge forming an ice dam of the Clark Fork River and creating glacial Lake Missoula.
The Lake Pend Oreille basin was carved by the repeated advances of Pleistocene ice and scoured by ice age floods. With the waning of ice age flood waters, the basin was, and continues to be, filled with glacial outwash and flood deposits. The lake is dammed at the south end by thick glacial and flood deposits the mark the beginning of the “Outburst Deposits”.
Farragut State Park is located at the “breakout” of Glacial Lake Missoula floods, where the ice dam in the Clark Fork valley and the 20-mile-long tongue of ice occupying the Lake Pend Oreille basin failed. From there, a torrent of water and ice burst from the south end of the lake. Located on the southern tip of Lake Pend Oreille in the Coeur d’Alene Mountains of northern Idaho, Farragut State Park offers unique scenery, history and an abundance of recreational opportunities.
South of Lewiston, Idaho, in the Tammany Bar area, there are private gravel quarries in coarse gravel terraces, which were formed by the Bonneville Flood, which happened in ~11months, sometime around 18.,500-17,400 years ago. Capping the gravels are rhythmites of sand and silt from the Missoula Floods.
