At the close of the Miocene, deformative movements were very widespread in the Rocky Mountains and between the principal development of the Coast ranges of California and Oregon, and mountain-making movements, new or renewed, were somewhat general in the west.
Subsequent erosion has changed the details of topography on an extensive scale, and subsequent deformative movements have renewed large topographic features where erosion had destroyed those developed by the close of the Miocene.
The careful study of these fluvial formations is likely to throw much light on the history of the deformative movements and changes in topography in the United States during the late stages of geological history.
Deformative movements of the minor sort seem to have been in progress somewhat generally during the Tertiary periods, especially in the western part of the country, but those at the close of the Pliocene seem to have exceeded greatly those of the earlier stages.
Deformative movements resulting in close folding were not common at this time, but such movements affected some of the coast ranges of California.