From introduction: The geologic record of the Tertiary period in the Green River Basin of southwestern Wyoming consists, in a broad way, of two quite different parts. The history of the first part, lasting through the Eocene epoch and perhaps on into the early Oligocene, was recorded in a thick series of sedimentary rocks of fluviatile and lacustrine origin. The history of the second part was recorded chiefly by successive stages of stream planation and stream trenching, but also in part by fluviatile sedimentation and, in certain localities, by glacial deposits. The first part of the record is virtually continuous, though its interpretation is by no means simple and obvious. The second part of the record is distinctly fragmentary, and the evidence the fragments provide is difficult to evaluate and to integrate.