PRESENT SCENE AND PRE-FRANCISCAN HISTORY 419 



The history is a long one, extending from possibly the Paleozoic period 

 to the present, and a very complex one, comprising the phenomena of 

 sedimentation, erosion, metamorphism, orogeny, and perhaps epeirogeny. 



Pre-Franciscan History 



coast complex 



The Coast complex consists of crystalline rocks, chiefly metamorphic, 

 including marble, quartzitic schists, mica-schists, gneisses, and granite. 

 The granite is intruded in the others and did not share their experience 

 of profound metamorphism. The marble and schists constitute a sedi- 

 mentary series. The gneisses may in part or whole have had an igneous 

 origin. The whole has suffered deformation in a deep zone of flow, re- 

 sulting in structural and mineralogical changes which to a great extent 

 obscure the original characters of the rocks. Fairbanks * has described 

 the series somewhat in detail under the name " basement complex." 

 This term is aptly applied, as the Coast complex is the intricate mosaic 

 at the base of the geologic column in the Coast ranges. 



The age of the Coast complex can only be vaguely guessed. It is long 

 pre-Cretaceous ; it may probably be Paleozoic. The former statement 

 follows from the age of the succeeding Franciscan rocks, which are either 

 Eo-Cretaceous or Jurassic. The Paleozoic date is an inference on the 

 uncertain grounds of lithologic and structural similarity to the meta- 

 morphic complex of the Sierra Nevada. 



The oldest rocks of the Coast complex were sediments, either calca- 

 reous muds or quartzose sands. The region of their accumulation was 

 therefore marine, but not so remote from land as to escape terrigenous 

 deposits. Land was probably near, since the sediments were buried to 

 that depth which conditions deformation-by-flow and recrystallization, 

 and zones of such great accumulation of sediment are usually shore zones. 



PRE-FRANCISCAN EROSION 



Pebbles of gneiss and granite from the Coast complex chiefly compose 

 the basal Franciscan conglomerate. These rocks had become surface 

 rocks at the inception of the Franciscan epoch. The elevation of the 

 folded and schistose gneisses from the zone of deformation-by-flow in- 

 volved orogenic or epeirogenic movements vertically of great amount, 

 and corresponding erosion of the mass. Thus in some pre-Cretaceous 

 epoch a land area succeeded to the sea in this region, and in Franciscan 

 time its shore closely approximated the position of the present shore. 



* Review of our knowledge of the geology of the California Coast ranges. Bull. Geol. Soc. Am., 

 vol. 6, pp. 78-82. 



