Contents

29 September 1989
Vol 245, Issue 4925

About The Cover

Along the eastern side of the Spring Mountains, Nevada, rocks of the Cambrian Bonanza King Formation (·530 million years old; gray cliffs on left) overlie overturned red beds of the Triassic and Jurassic age (·200 million years old) along the Keystone trust, one of a series of major thrust faults in the eastern Great Basin. The amount of displacement on these thrust faults must be accounted for in order to restore the older rocks to their original geographic positions. See page 1454. [Photograph by N. Cristie-Blick]