THE PLIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 343 



California. — In the Pliocene of the Pacific coast ^ a change to colder 

 conditions is indicated both by the disappearance of warm-temperate t>TDes 

 of plants and by the colder character of the salt water fauna, as well as of 

 that found in the freshwater Pliocene lake beds. The whole west coast 

 of North America was rising and the shore receding westward ; the waters of 

 the Pacific no longer reached the foot of the Sierra Nevadas, nor even the 

 great central valley between the Sierra Nevadas and the Coast Range; 

 but elevation was not uniform, for valleys of the coast ranges that had been 

 eroded during the Miocene were filled Avith sediments during the Pliocene; 

 the enormous deposits to a depth of 3,000 feet of the Great Valley be- 

 tween the Sierras and the Coast Range belong partly to the Pliocene and 

 partly to the Quaternary, an area wholly of fluviatile origin. Thus during 

 the Pliocene the Sierra Nevadas were elevated, and California at that 

 time was very much like the California of to-day; with the great moun- 

 tain ranges of the Sierras on the east, the long, broad valley — in many 

 cases covered by freshwater lakes — in the center, and on the west the 

 long, low Coast Range. 



The Pliocene Flora 



The eastward trend of the deciduous tree flora of Europe is a most 

 significant fact. It has been pointed out above that the Miocene and 

 Pliocene forest trees of Europe become the modern forest trees of our Cen- 

 tral and South Atlantic states. With the flora in late Tertiary times there 

 came certain faunal waves. Unfortunately nothing is known of the flora 

 of the Great Plains region nor of the central mountain region, and we 

 must rely upon observations made in California, from which only indirect 

 conclusions can be drawn. 



Flora of California. — Here we must rely upon the earlier notes of 

 Lesquereux (1859-1888) and of Turner (1891). 



Plants of the auriferous gravels of the Sierra Nevada^ collected in Nevada 

 County, California, on the thirty-ninth parallel indicate a temperature a 

 few degrees higher on the average than that of middle California of the 

 present day ; in other words, they represent a latitude a few degrees farther 

 south. Thus in Nevada County on the thirty-ninth parallel in Pliocene 

 times there lived palms similar to those which now flourish in California on 

 the thirty-fourth parallel. Pliocene i^alms are, however, very rare, only a 

 single specimen of a sal^al being found in the whole collection from Nevada 

 County. The prevalence of a warmer climate than the present in Pliocene 

 times seems to be indicated by oaks of Mexican type and by species of figs 

 (Ficus), but this is counterbalanced l)y the presence of the ])irch {Betula), 



' Smith, J. P., Saliont Events in the Geologic History of California. Science, u.s., Vol. 

 XXX, no. 7f>7, 1909, pp. .346-351. 



- Lesquereux, L., Report on the Fossil Plants of the Auriferous Gravel Deposits of the 

 Sierra Nevada. Mem. Mtis. Comp. Zoiil. Camhrklije, Mass., Vol. II, 1S82. 



