A Pliocene flora from the Coast Ranges of California 
HAROLD HANNIBAL 
(WITH PLATE I5) 
GENERAL REMARKS 
The origin and development of the California floras, par- 
ticularly the peculiar xerophytic chaparral, has been a problem of 
no small ‘nterest to students of phytogeography. The occur- 
rence in the Coast Ranges of a recognizable Pliocene flora, the 
only thing of its kind known in North America consisting entirely 
of living species, partly mesophytic and partly xerophytic in 
character, throws an interesting light upon the antiquity of these 
floras and suggests a possible explanation of the isolation of 
boreal and arctic plants on the upper slopes of high mountains 
of the state far south of their normal ranges. 
THE SANTA CLARA FORMATION 
WorK OF PREVIOUS WRITERS 
The Santa Clara formation was named and described by 
Cooper! in 1894. The deposit was considered to be of lacustrine 
origin and referred to the Pliocene on the basis of its general 
lack of consolidation, the gentle tilting of the beds, and the large 
percentage of recent species in the molluscan fauna. It had been 
previously described in some detail by Lawson,’ however, who also 
regarded it as Pliocene in age, but of delta origin. The portion 
lying in the Santa Cruz Quadrangle has been discussed by Arnold * 
and again by Branner, Newsom, and Arnold,‘ its distribution 
being shown in map form. Recently Jones,° solely on lithological 
grounds, has tentatively suggested its contemporaneity with what 
has been termed by Lawson and Palache® as the Orindan forma- 
1 Proc. Calif, Acar: Sci. 4°) 17%. 
2 Bull. Dept. Geol. Univ. Calif. 1: 1 i 1893. 
3 Proc. U. S. Nat. Mus. 34: 355. 1908. 
4Santa Cruz Folio, U. S. Geol. Surv. 6. 1909. 
5 Bull. Dept. Geol. Univ. Calif. 6: 71. 191. 
6 Bull. Dept. Geol. Univ. Calif. 2: 371. 1902. 
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