The Geological Sfory Briefly Told 77 



lifted into a low mountain range, and during Eocene time (early 

 Tertiary) remained a low mountain range undergoing erosion. 

 After a prolonged interval of elevation and erosion the Coast 

 Ranges began to sink, and continued to sink till nearly or quite 

 all of the central and southern portions were beneath the Pacific 

 Ocean. During the Martinez epoch (of the Eocene period) 

 more than 2,000 feet of sandstone and shale were accumulated. 

 The Martinez epoch was interrupted and deposition terminated 

 by earth disturbance and uplift. During the succeeding epoch, 



. Photo by Ralph Arnold, U. S. Geol. Survey 



FIG. 21. Natural Bridge, in Monterey shale, three miles east of Santa 

 Cruz. Tidal waves cut a channel along a joint-plane in the shale. 



the Tejon, the land again subsided and was covered by a shallow 

 sea, and essentially the conditions that had prevailed in Martinez 

 time were re-established, but over a somewhat more widespread 

 area. Sediments to a thickness of 2,000 feet of sandstones and 

 shale were deposited in the shallow Tejon sea. The Tejon sub- 

 sidence and sedimentation was brought to a close by earth move- 

 ment and uplift. A considerable interval of erosion followed. 

 The next great geologic period is the Miocene, and the rocks 

 are known as the Monterey group. A widespread subsidence 



