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”
