Along the ICE AGE FLOODS
NATIONAL GEOLOGIC TRAIL

Lake Pend Oreille Ice Age Floods National Geologic Trail  The Purcell Lobe of the Cordilleran Ice Sheet repeatedly formed a 2000′ tall ice dam in this area, which backed up Glacial Lake Missoula and eventually burst catastrophically, releasing Ice Age Floods as often as about every ~10-60 years. Lake Pend Oreille is the largest lake in Idaho. The lake level is 2062 ft above sea level, with the surrounding terrain as high as 6002 ft. With a maximum depth of 1150 ft, this lake is the 5th deepest in the US. The location of the lake is probably related to an old river valley controlled by faults. The Lake Pend Oreille basin was carved by the repeated advances of Pleistocene ice and scoured by Ice Age Floods. With the waning of flood waters, the basin was filled with glacial out-wash and flood deposits. The lake is dammed at the south end by thick glacial and flood deposits that mark the beginning of the “Outburst Deposits”Quick Facts MANAGED BY:US Forest Service

Farragut State Park Ice Age Floods National Geologic Trail 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. Farragut State Park is located at the “breakout” of Glacial Lake Missoula floods. Failure of the ice dam in the Clark Fork valley fractured and broke apart the 20-mile-long tongue of ice occupying the Lake Pend Oreille basin, and a torrent of water and ice burst from the south end of the lake. That churning slurry of flood waters, ice, boulders and other debris erupted from the south end of Lake Pend Oreille, flowing 2000 ft deep across Farragut State Park. Nearly all of the water escaping from Glacial Lake Missoula passed through this area. Discharge estimates range from 14 to 21 million cubic meters per second! Vic Baker’s definition of a megaflood is one which has a discharge of at least 1mil cubic m/s, so we are possibly looking at ground zero for the worst Pleistocene flood in the world. Farragut State Park includes many geologic features left by glaciation and megafoods.Hoodoo channel, an abandoned outlet of Lake Pend Oreille provided a pathway for late-glacial meltwater and for the last outbursts from Glacial Lake Missoula. The channel is marked with a number of closed depressions, probably the result of melting icebergs. One of the largest of these features have been proposed, including kettles, potholes, and sub-glacial meltwater. Some of that debris was deposited to form the Rathdrum Prairie Outburst Plain, an extensive, heterogeneous mix of flood deposits. Farragut State Park offers unique scenery, history and an abundance of recreational opportunities. Quick Facts Location:13550 E. Hwy 54 Athol, ID 83801 

Green Monarch Ridge Ice Age Floods National Geologic Trail THIS IS WHERE IT ALL BEGAN! The Green Monarch Ridge viewpoint, just south of the Hope Fault, is positioned along the edge of the Purcell Trench Ice Lobe. Here it was responsible for damming the mouth of the Clark Fork drainage basin. This damming effect resulted in the formation of Glacial Lake Missoula, the source of the waters for much of  the PNW Pleistocene Ice Age Floods. 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, located approximately 10 miles south of this viewpoint. Grinding and scraping, the Purcell Trench Ice Lobe backed up behind the Green Monarch Ridge, eventually building an ice plug up to 4,000 feet thick, and scouring out the deepest parts of Lake Pend Oreille. The Purcell Trench Ice Lobe divided into four sub-lobes: one went approximately west (US Highway 2), two went south (US Highway 95 and Lake Pend Oreille) and one went east (SR 200). All four sub-lobes contributed to blocking the Clark Fork drainageQuick Facts MANAGED BY:US Forest Service – Idaho Panhandle National Forest