144 OUTLINE OF PLANT GEOGRAPHY 



Pickeringia, Chamaebatia, Adenostoma, Bolandra, Carpenteria, 

 Eucharidium, Hemizonia, and many others. 



The inner valleys of southern California are as a rule arid, and 

 often actual deserts. South of the Tehachipi Mountains, which 

 form the southern boundary of the great central valley, lies the 

 Mojave desert, which is a plateau of 3,000 to 4,000 feet elevation 

 toward the west, but descending on the east to the Colorado River. 

 To the southeast lies Death Valley, a region of intense heat 

 which lies more than 300 feet below sea-level and is the lowest 

 point in the United States. 



In the more elevated portion of the Mojave desert, which is 

 traversed by the railway, the traveller's attention is at once 

 attracted by the fantastic tree-yuccas (Yucca brevifolia), scattered 

 over the landscape. With these are found in places scrub junipers 

 and some other shrubs. Cacti are scarce, in marked contrast to 

 the Colorado desert to the south, which is separated from the 

 Mojave by the San Bernardino mountains. 



In the Mojave the predominant shrub is the creosote-bush 

 (Larrea Mexicana) , also a feature of the Colorado desert. With it 

 are associated a number of other characteristic species, e. g., Fran- 

 seria dumosa, species of Atriplex, Opuntia, Ephedra, Euphorbia, 

 Lepidium, Gilia, Eschscholtzia and others. 



Along the Mexican boundary. in southeastern California and 

 Arizona, is the Colorado Desert, a region with a vegetation dis- 

 tinctly Mexican in type, which will be discussed more in detail 

 later. 



While the floor of the great valley is largely destitute of trees, 

 especially in the southern areas, the banks of the rivers and smaller 

 streams are more or less heavily wooded. Sometimes, as along 

 parts of the Sacramento, extensive bottom lands are developed, 

 which support a quite heavy forest of large cotton-woods, and 

 elsewhere along the streams are willows and alders. 



Sometimes the western sycamore (Platanus racemosa) is found 

 along the stream-banks, especially toward the south, and the 

 box-elder (Acer Negundo) is a common and wide-spread species. 

 Less common is the Calif ornian walnut (Juglans Calijornica). 

 Roses, blackberries, poison oak (Rhus), dogwood, button-bush 

 (Cephalanthus) are the commonest shrubs of the stream-side 

 thickets. 



