The area that was covered by Lake Agassiz was the geographic center of North America. Its extent was about from 45° 30' to 55° of north latitude, and from 92° 30', on the international boundary, to 106°, on the Saskatchewan River.
- Perkins S. 2002. Once Upon a Lake. Science News. 162 (18): 283–284.
- Keating, William H. (1824). Narrative of an Expedition to the Source of St. Peter's River, Lake Winnepeek, Lake of the Woods, …. vol. 2. Philadelphia, Pennsylvania, U.S.A.: H.C. Cary & I. Lea. p. 7.
|volume=has extra text (help) From p. 7: "In some places pebbles were as abundant as if we had been travelling upon the bed of some former river or lake; the mind endeavours in vain to establish limits to the vast expanse of water which certainly at some former day overflowed the whole of that country."
- Upham, Warren (1880). The Geology of Central and Western Minnesota. A Preliminary Report. [From the General Report of Progress for the Year 1879.]. St. Paul, Minnesota, U.S.A.: The Pioneer Press Co. p. 18. From p. 18: "Because of its relation to the retreating continental ice-sheet it is proposed to call this Lake Agassiz, in memory of the first prominent advocate of the theory that the drift was produced by land-ice."