This narrative history of geologic and biologic events in the Great Plains had its origin in a study intended to identify potential National Natural Landmarks in the Great Plains, commissioned by the National Park Service. William A. Cobban, G. Edward Lewis, and Reuben J. Ross of the U. S. Geological Survey were collaborators in that study, and some of their contributions to the history of life on the Great Plains have been incorporated into this narrative, which was undertaken at the urging of Wallace R. Hansen. The photographic illustrations, other than those obtained from the film library of the U. S. Geological Survey, were provided by the interest and effort of my friends and colleagues of the Geological Survey—including C. R. Dunrud, V. L. Freeman, C. D. Miller, R. D. Miller, F. W. Osterwald, R. L. Parker, W. H. Raymond, III, Kenneth Shaver, and R. B. Taylor—and by Eugene Shearer, Intrasearch, Inc., Denver, Colo. Without their help this publication would not have been possible. SOME SOURCE REFERENCES Alden, W. C., 1932, Physiography and glacial geology of eastern Montana and adjacent areas: U. S. Geological Survey Professional Paper 174, 133 p. Bluemle, J. P., 1977, The face of North Dakota—the geologic story: North Dakota Geological Survey Education Series 11, 73 p. Colton, R. B., Lemke, R. W., and Lindvall, R. M., 1961, Glacial map of Montana east of the Rocky Mountains: U. S. Geological Survey Miscellaneous Geologic Investigations Map I-327. Colton, R. B., Lemke, R. W., and Lindvall, R. M., 1963, Preliminary glacial map of North Dakota: U. S. Geological Survey Miscellaneous Geologic Investigations Map I-331. Curtis, B. F., ed., 1975, Cenozoic history of the southern Rocky Mountains—Papers deriving from a symposium presented at the Rocky Mountain Section meeting of the Geological Society of America, Boulder, Colorado, 1973: Geological Society of America Memoir 144, 279 p. Darton, N. H., 1905, Preliminary report on the geology and underground water resources of the central Great Plains: U. S. Geological Survey Professional Paper 32, 433 p. Flint, R. F., 1955, Pleistocene geology of eastern South Dakota: U. S. Geological Survey Professional Paper 262, 173 p. Frye, J. C., and Leonard, A. B., 1965, Quaternary of the southern Great Plains, _in_ Wright, H. E., Jr., and Frey, D. G., eds., The Quaternary of the United States—A review volume for the 7th Congress of the International Association for Quaternary Research: Princeton University Press, p. 203-216. Howard, A. D., 1958, Drainage evolution in northeastern Montana and northwestern North Dakota: Geological Society of America Bulletin, v. 69, no. 5, p. 575-588.