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.