The Geological Story Briefly Told 



75 



which must have been very long, is a "lost interval" so far as 

 any record is preserved in the rocks. The Cretaceous, which 

 overlies, rests "unconformably" upon the old eroded landscape. 

 The fact that deposits of Knoxville time are largely shales, with 

 very little sandstone or conglomerate, indicates a shallow sea 

 into which sediments were borne from lands of low relief. The 

 region extending from the Sierras to the Coast Ranges is thought 

 to have been a sound, or series of sounds, with islands, similar to 

 the coast of Alaska and British America. The Cretaceous rocks 

 form one of the most important and widespread systems of the 

 Pacific Coast. The Lower Cretaceous deposits (Knoxville) 

 occur from central Oregon to southern California, while the 

 Upper Cretaceous (Chico) , which is still more widespread, ex- 

 tends from Vancouvers Island to the Peninsula of Lower Cali- 

 fornia. Thus a vast area of the present State of California, 

 including the region of the Coast Ranges, was under water. 



Photo by W. C. Mendenhall, U. S. Geol. Survey 



FIG. 20. Devil's Kitchen. San Emigdio Canyon, looking east across the 

 canyon. Oligocene formation. The sharp peak at the right is Eagle Rest. 



Long Subsidence and Sedimentation 

 in Coast Range Region 



Subsidence continued through Lower Cretaceous (Knox- 

 ville) time, the bottom of the shallow sea slowly subsiding as 

 sediments continued to be spread upon its bottom till shale and 

 sandstone had accumulated to depths of 3,000 to 4,000 feet in 

 the San Luis region, and in the Coast Ranges north of San 

 Francisco Bay the deposits have a measured thickness of between 



