RERTIARY FAUNAS OF THE PACIFIC COAST 515 
the deposition of the Chico were accompanied by basic igneous 
intrusions. No profound movements and no volcanic activity 
accompanied the post-Chico (post-Cretaceous) movements in Cali- 
fornia as they did in Washington. 
Steep mountains bordered the youthful Eocene sea in southern 
Oregon, northeastern California, and north of San Diego, and 
occupied portions of one or more large islands in the region of Mon- 
terey and Santa Barbara counties south of San Francisco. Elsewhere 
the relief of the land appears to have been comparatively low and the 
shore-lines with few bays or estuaries. 
DISTRIBUTION AND CHARACTER OF SEDIMENTS 
Rocks of marine origin and Eocene age are found at many local- 
ities throughout Washington and Oregon west of the Cascade Range, 
and over considerable areas of the Coast Ranges in central and 
southern California. Although Eocene rocks probably once fringed 
the greater part of the western base of the Sierra Nevada, they are 
now all removed by erosion or covered by later formations except at 
one locality near Merced Falls. For the most part the Eocene rocks 
of the Pacific Coast are either sandstone or shale. Conglomerate is 
found at the base of the formation throughout southeastern Oregon, 
north of San Diego, and at a few localities along the northeastern 
flanks of the Coast Range; and at Port Crescent, Washington, 
Eocene fossils are associated with tuff; but these occurrences are 
exceptional. Also, diatomaceous shales occur at the top of the 
Eocene series in the vicinity of Coalinga, Cal., where they are believed 
to be the source of important deposits of petroleum. Coal and 
other indications of shallow- and brackish-water conditions are 
found over much of Washington and Oregon and California, usually 
overlying marine Eocene beds. ‘The maximum thickness of the 
Eocene sediments varies from 8,500 feet east of the Cascades,? 
10,000 to 12,000 feet in western Oregon? to gooo+ feet in southern 
California. 
CONDITIONS PREVAILING DURING THE EOCENE 
During the early part of the Eocene, marine conditions prevailed 
over a considerable territory that later was covered by brackish- or 
1G. O. Smith, Mt. Stewart Folio. 
2J.S. Diller, Roseburg, Coos Bay, and Port Orford Folios. 
3 Ralph Arnold, U. S. Geol. Surv. Bull. 321, p. 21. 
