It was designated as a National Natural Landmark in 1966 because it contains the great ripples (often measuring 25 to 50 feet (7.6 to 15.2 m) high and 300 feet (91 m) long) that served as a strong supporting element for J Harlen Bretz's contention that Washington State's Channeled Scablands were formed by repeated cataclysmic floods over only about 2,000 years, rather than through the millions of years of erosion that had been previously assumed.

[2][3] The lake was the result of an ice dam on the Clark Fork caused by the southern encroachment of a finger of the Cordilleran ice sheet into the Idaho Panhandle (at the present-day location of Clark Fork, Idaho, at the east end of Lake Pend Oreille).

The height of the ice dam typically approached 610 metres (2,000 ft), flooding the valleys of western Montana approximately 320 kilometres (200 mi) eastward.

The cumulative effect of the floods was to excavate 210 cubic kilometres (50 cu mi) of loess, sediment and basalt from the channeled scablands of eastern Washington and to transport it downstream.

[5] These floods are noteworthy for producing canyons and other large geologic features through cataclysms rather than through more typical gradual processes.

In addition, Middle and Early Pleistocene Missoula flood deposits have been documented to comprise parts of the glaciofluvial deposits, informally known as the Hanford formation that are found in parts of the Othello Channels, Columbia River Gorge, Channeled Scabland, Quincy Basin, Pasco Basin, and the Walla Walla Valley.

Based upon these criteria, Quaternary geologists estimated that the oldest of the Pleistocene Missoula floods happened before 1.5 million years ago.

The older Pleistocene glaciofluvial deposits within the Hanford formation are fragmentary in nature because they have been repeatedly eroded and largely removed by subsequent Missoula floods.

[8] The ice dam reached east up the Clark's Fork to Cabinet, Montana, and southward around the mountain to Bayview, Idaho on the south tip of Lake Pend Oreille in Farragut State Park.

Possibly, glacial sediment, rock flour, suspended in the turbid lake water which created an hostile aquatic habitat for fish.

In addition, fossils of large mammals (megafauna), i.e.; mammoths, mastodons and bison which may have roamed nearby, not been found.