In 1898, Frank Charles Schrader undertook a study of the Copper River Basin for the United States Geological Survey (USGS).

Based on sedimentary evidence, he concluded that there was a possibility of a large body of standing water being responsible for the deposits and that this could have been an arm of the sea.

[5] In 1954, Fred Howard Moffit noted that topographic conditions were favorable for the possibility of a large lake, but that specific evidence was lacking at that time.

[8] During the Wisconsin glaciation, a multitude of glaciers extended into and blocked drainage exits from the Copper River Basin.

[10] The highest surface level the lake achieved was 975 m (3,199 ft), based on sedimentation in the northwestern area of the basin.

[15] In 2005, Michael Wiedmer, then a biologist at the Alaska Department of Fish and Game, was shown the carcass of a pygmy whitefish which had been collected from Lake George.

[18] Wiedmer's research suggested the possibility of Lake Atna being a serial generator of megafloods from glacial dam failures.

[19] One such possible flood originated from a catastrophic failure of a glacial dam 61 m (200 ft) in height at Tahneta Pass,[3] located at the eastern end of Matanuska Valley.

[3] Diamicton, glacial, glaciolacustrine, and lacustrine origin deposits exist in many areas of the Copper River Basin.

[9][22] All major rivers present today occupy narrow valleys that have cut up to 137 m (449 ft) into the bottom of the basin.

[10] The postulated Matanuska Valley flood produced by Lake Atna 17,000 years ago[17] may have been responsible for the deposition of a thin stratum of clay and silt grains in the Anchorage area.