be derived from this third geo-flora. These would include such gen- 

 era as California Bay (Umbellularia califomica, Lauraceae), flannel 

 bush {Fremont odendron spp., Sterculiaceae), and California Fan 

 Palm ( Washington ia filiferd) . 



Recent Changes in the Flora 



The present-day CaHfornia vegetation and flora trace their 

 history back several tens of millions of years into early Tertiary 

 times. Man has been in California a brief period of time. How- 

 ever, man himself has been responsible for several drastic and 

 rapid alterations in the flora of California which are paralleled 

 in magnitude only by the long-term changes that occurred slowly 

 in response to geological and climatic changes in past geological 

 times. The changes that the Indians brought about in the native 

 flora are unknown, although the burning practices carried on by 

 several Indian groups undoubtedly had an important local effect 

 in eradicating certain native species and encouraging others. The 

 present distribution of the native northern California walnut 

 (Juglans hindsii) is undoubtedly partly due to the California 

 Indians' practice of carrying the edible nuts of this species from 

 place to place. Many individual specimens or small colonies of 

 this rather uncommon tree are located at the sites of former 

 Indian campsites in the region to the north and east of San Fran- 

 cisco Bay, although the degree to which the present distribution 

 of this tree has been influenced by the activities of Indians is 

 still a matter of contention. 



Another change in the flora has been the extinction by man 

 of a few plant species and the reduction of other species to a few 

 or perhaps only a single known population as a result of urbani- 

 zation or development of agricultural lands. Many rare species, 

 such as Large-Flowered Fiddleneck {Amsinckia grandi flora, Bora- 

 ginaceae), Hickman's Mallow (Sidalcea hickmanii, Malvaceae), 

 Catalina Ironwood {Lyonothamnus floribundus , Rosaceae), and 

 Pale Brodiaea (Brodiaea pallida, Amaryllidaceae), have been rare 

 since they were first brought to the attention of biologists and 

 are rare for natural rather than man-made causes. Such restricted 

 species naturally attract the attention of conservationsts. Yet a 



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