In this study, nine florules from the Chloropagus Formation near Fernley, Nevada, are dated at 14.7-13.4 million years. The author finds that dominant mixed conifer forest and sclerophyll woodland species of the Sierra Nevada-Klamath region replaced exotic deciduous hardwoods in the two lowest sites. He concludes that this change reflects the loss of adequate summer rain as upwelling from a colder ocean resulted from spreading East Antarctic ice.

Additional title page description: A study of the Green River Formation in a 2,300-square-mile area in northeastern Utah and northwestern Colorado.