The Geological Story Briefly Told 



83 



is 100 feet above sea level rises progressively to over 400 feet at 

 Tunitas Creek 10 miles south. This shows that uplift pro- 

 gressed differentially southward, and not at the same rate at 

 all points. At Fort Ross, 60 miles north of San Francisco Bay, 

 a series of wave-cut terraces occurs marking successive uplifts 

 of the short at 280, 350, 440, 760, 1,180, 1,400 and 1,520 feet 

 above the present waves. Near Kenney, in northwestern Men- 



Photo by G. W. Stose, U. S. Geol. Survey 



FIG. 23. Wave-cut terraces, San Luis Obispo Bay. The upper beach is 

 100 feet above sea-level; the middle one is sixty feet; and the lowest one is 

 ten feet. 



docino County, wave-worn pebbles lie on a wave-cut beach 

 1,200 feet above sea. Farther north in Humboldt County the 

 uplift as shown by the elevated terraces is 1,600 to 1,700 feet. 



A Lake or Inland Sea Covers Central 

 Great Valley 



Where is now the Great Valley of California was a vast lake 

 or inland body of water, into which poured the waters of the 

 rivers from the western slope of the great Sierra uplifted block, 



