INTRODUCTION 



ORIGIN, DISTRIBUTION, AND CHARACTERISTICS OF 

 THE YOSEMITE FLORA. 



WERE it permitted us to view the Sierra Nevada as 

 they appeared in past geologic times, we would see 

 that at one period they were the workshops of 

 mighty glaciers which, like powerful giants, were 

 grinding down the mountains, hewing out Yosemites, polish- 

 ing domes, and converting solid rock into fertile soil. As one 

 prepares a field before the time of sowing, so, in the glacial 

 period, these titanic forces were preparing the way for the forests, 

 the meadows, the flowery fields yet to come. For in those early 

 days our region was devoid of ordinary vegetation, being entirely 

 under the influence of ice and snow. Finally, as conditions 

 changed, the glaciers, having completed their work, retired to 

 the slopes of the highest peaks and their places were taken by 

 trees and shrubs, grasses and flowers, as we now find them. It 

 may be of interest to consider briefly the origin of this flora. 



The present vegetation of the Yosemite National Park has been 

 derived from at least three sources. One element had its origin 

 in the lowlands of California, where it still flourishes, sending 

 representatives, like the species of Ceanothus, Manzanita, and 

 Yerba Santa, up through the foothills to the warmer parts of our 

 district. A second group of species reaches us from the desert 

 borders on the east. These had their origin in the Mexican 

 Region from which they gradually spread northward, finally 

 crossing the Sierran passes to flourish at a few places on the 

 westerly slope. The Sagebrush is doubtless one of these, and 

 even the Pinon Pine of the desert ranges has been recently found 

 on a branch of the Tuolumne. The third, and by far the most 

 important element in our flora, is the boreal. It is a generally 

 accepted theory that during the glacial period species belonging 

 normally to Arctic regions were compelled to migrate southward, 

 on account of the great reduction in temperature. At the close 

 of the glacial period conditions were reversed, and these northern 

 species, now finding the climate gradually growing warmer and 

 warmer, were forced to recede to colder regions and not only 

 migrated back to the North but also retreated to the mountains, 

 where they found conditions somewhat similar to those of their 

 original northern home. It is not surprising, therefore, to find 

 many Sierran plants occurring, almost without modification, in 



