THREATENED ARIDITY ON THE PACIFIC SLOPE 179 



em California. On the west slopes of the San Bernardino 

 and San Jacinto ranges, its main body of growth is above the 

 4,000-feet contour line. Below this the tree thins out rapidly, 

 and at elevations of 3,000 feet practically ceases. In the San 

 Gabriel mountains it begins to grow at elevations of 1,000 feet 

 above sea-level ; at 3,000 feet it forms very numerous groves 

 in the midst of the chaparral. Now, there are the clearest evi- 

 dences that not very far back in time a nearly uniform forest of 

 this species covered many of the slopes of the San Gabriel moun- 

 tains between the 2,000-feet and 3,000 feet contour levels. The 

 numerous single trees and old stumps in the chaparral are the 

 remnants of this growth. Moreover, when the big cone fir is 

 burned out on the slopes below the 4,000-feet level, neither it 

 nor any other species of conifers reforest the denuded areas, show- 

 ing that conditions exist which are inimical to forest growth. 

 In the San Bernardino and San Jacinto ranges the lower edge of 

 the big cone fir forest is tolerably compact and well defined. The 

 outlying patches on the slopes that one sees so frequently in the 

 San Gabriel are lacking. The extensions from the main body of 

 growth are along the streams and gorges where abundant moist- 

 ure exists. The San Bernardino and San Jacinto mountains are 

 farther from the ocean than the San Gabriel; hence for same 

 elevations they do not receive so heavy a precipitation, and have 

 in consequence a higher limit for the lower edge of the range of 

 the big cone fir. The San Gabriel mountains, being nearer the 

 ocean, receive a greater precipitation ; hence have an ulterior 

 limit for the inferior edge of the big cone fir at a considerably 

 lower elevation than the other two ranges ; but the lack of re- 

 forestation on areas where the growth is destroyed and the many 

 detached patches below the main body of growth prove that 

 the species is retreating toward regions of greater humid it}'. As 

 the process is aided and accelerated by forest fires of modern 

 date, another generation will not pass before the lower limit for 

 the growth of the tree in the San Gabriel mountains will be at 

 quite as high altitude as it is in the San Bernardino and San 

 Jacinto ranges. In comparison with the allied northern Pseu- 

 dotsaga mucronata, or red fir, the species is more definite in cone 

 and seed production. 



The redwood is a tree of extreme susceptibility to temperature 

 and humidity conditions, and apparently possesses a very low 

 ra tio'of adaptal >i 1 1 ty. It ranges along the California coast from Los 

 Angeles county to the northern boundary of the state and across 



