98 Adventures in Scenery 



close of the Palaeozoic era and ushered in the Mesozoic era the 

 rocks were tilted and eroded. Then later formations were 

 deposited upon their up-turned edges. The rocks were again 

 upheaved and folded in Triassic time. The great upheaval 

 which occurred about the close of the Jurassic period raised all 

 of northern California above the sea. It is thought that islands 

 had existed in this region since very early Archaean time, but 

 the great uplift which marked the close of the Jurassic period 

 extended the land area far to the northwest into the Pacific 

 Ocean west of Cape Blanco. Just how far the land extended 

 beyond the present coast line is not known. 



During the Cretaceous period the land sank again so that 

 the sea covered the land where are now the Klamath Mountains 

 and much of the coast ranges. The Sierra Nevada Range re- 

 mained above the sea. The Chico formation, the earliest Cre- 

 taceous deposit, was deposited along the western base of the 

 Sierra Nevada Range and around its northern end. The Pacific 

 Ocean covered most of the region about Lassen Peak and Mount 

 Shasta, and extended far into Oregon. The Chico is the oldest 

 of the sedimentary rocks that overlie the bent, folded, and 

 crumpled Palaeozoic rocks, the auriferous (gold-bearing) 

 slates. There is marked "unconformity" between the old 

 Palaeozoic rocks and the overlying horizontal rocks. The 

 older (Palaeozoic) rocks, which are bent, folded and much 

 metamorphosed by the heat and pressure of the mountain- 

 building processes, contain the gold-bearing rocks from which 

 the "auriferous gravels" have come. 



At the close of the Cretaceous period the Klamath Moun- 

 tains were again raised above sea level, and the Cretaceous 

 (Chico) strata which had been laid down as horizontal sedi- 

 ments were much folded and broken. A large part of the 

 Chico beds thus exposed to erosion were washed off the land. 

 The land of what is now northern California was long subjected 

 to weathering and erosion, and was finally worn down nearly 

 to a plain (peneplain) . Streams had nearly reached base-level, 



