Geology of West Coast Region of United States 

 mineral representative of a particular class of 

 crystal symmetry, and further is known to occur 

 in no other locality in the world. As this locality 

 is largely worked out, it seems probable that the 

 mineral will assume additional value as a minera- 

 logical curiosity. 



Mercury is one of the most important products 

 of the Coast Range. Becker and Lindgren believe 

 it to have been formed at a later date than the 

 mineral deposits discussed above, and it is, there- 

 fore, included among the products formed during 

 the Cretaceous and later periods. 



Mineral Deposits in Cretaceous and Post- 

 Cretaceous Rocks. — These include products of 

 great value, such as oil, coal, borax, silver and 

 gold. Of these oil is the most important. It is 

 treated at length elsewhere in this volume. Geol- 

 ogists have long puzzled over the fact that enormous 

 quantities of oil are concentrated in the Tertiary 

 strata of southern California, while northern Cali- 

 fornia, Oregon, and Washington contain only rela- 

 tively small amounts of oil. A suggestion of Dr. 

 Branner possibly gives a clue in regard to this con- 

 centration. He has pointed out that an archipelago 

 existed in Tertiary times in the Pacific epiconti- 

 nental sea along the axis of the present Coast ranges 

 terminating in a cul-de-sac in southern California 

 with the opening towards the north. The cold 

 arctic currents which favored the development of 

 the diatoms, etc., were caught, and the diatomace- 

 ous material accumulated to the landw^ard of the 

 islands and in this bay. 



In the southeastern portion of California, east 

 of the Sierra Nevada Range and its continuations, 

 the sedimentation of the period occurred in lakes 

 rather than in the ocean. The character of the 

 deposits suggests that conditions of marked aridity 

 occurred throughout the Tertiary. The deposits 

 formed by evaporation include borax, nitrate, sodium 

 carbonate, salt, etc. The world's greatest accumu- 

 lation of borax occurs in ancient lake beds of prob- 

 able Miocene age. These beds are now turned up 

 on end, so that the miner considers them as ledges 

 rather than bedded deposits. The mining law is 

 applied according to this interpretation. Secondary 

 deposits have been leached from these strata, and 

 deposited by evaporation in present day lakes and 

 playas. 



Other economic products, concentrated under 

 the conditions of aridity, include not only sodium 

 and magnesium salts, but also those of potassium, 

 notably in the case of Searles Lake, San Bernardino 

 County, California. 



56 



