The Lava Plain of the North 97 



Shasta County, is regarded as the southern terminus of the Cas- 

 cade Range. Mount Shasta and Lassen Peak are immense lava 

 cones. Mount Shasta rises 14,401 feet above sea level. The 

 summit of Lassen Peak is 10,437 feet above sea. Their bases, 

 on the bottom of the ancient valley, are probably not much 

 above sea level. Mount Shasta, Lassen Peak, Butt Mountain, 

 Crater Peak, Burney Butte, and those at the head of Burney 

 Creek, as well as a host of smaller conical hills, are all ancient 

 volcanoes which contributed to the outflow of lava. 



The Klamath Mountains include the complex group of 

 mountain ranges which interrupts the Great Valley of central 

 California in the north. The rocks of this group of ranges are 

 much bent, folded, and crumpled. This group of mountains 

 forms a sort of connecting link between the Sierra Nevada, the 

 Cascade, and the Coast ranges. The Klamath Mountains are 

 located in part in Oregon, but mostly in California. The 

 Klamath Mountains are similar to the Sierra Nevada Range in 

 structure and character of rocks. They overlap the northern 

 end of the Coast Ranges in California, and so may be regarded 

 as belonging to the Coast Range system. 



Many Formations in Northern California 



Twenty-two geologic formations occur in this district of 

 California. Of these 1 3 are sedimentary rocks, that is, forma- 

 tions deposited as sediments in bodies of water. The remaining 

 nine are igneous; emitted as molten lava or ejected as volcanic 

 ash. This region of northern California and western Oregon was 

 covered by the sea in the Silurian, Devonian, and Carboniferous 

 periods of the Palaeozoic era, and till the close of the Jurassic 

 period of the Mesozoic era. Marine sedimentary rocks having 

 a total thickness of more than four and a half miles accumu- 

 lated during this long time. These rocks, although laid down 

 in horizontal position, have since been folded, crumpled and 

 metamorphosed. Fissures in the rocks have been filled with 

 gold-bearing quartz veins. In the upheaval which marked the 



