1913J Grinnell -Swarth: Birds and Mammals of San Jacinto 215 



LIFE AREAS OF THE REGION 



The distribution of each one of the species of vertebrate 

 animals inhabiting the San .Jacinto area appears to respond to 

 the influence of at least three entirely different orders of ecolog- 

 ical delimitation. These three kinds of control are indicated by 

 the adjectives: zonal, faunal. and associational. The conceptions 

 involved in each are probably not subject to precise definition; 

 at any rate we do not find it feasible even to attempt such treat- 

 ment with the limited data thus far accumulated. In each case 

 the genera] notion may be conveyed by the citation of instances, 

 and by mere suggestions as to causative factors. 



Life Zones 



The concept of life zones has been the most commonly recog- 

 nized of the three. The various factors involved have been 

 exhaustively discussed by C. II. Merriam, in his various papers, 

 notably the one giving the results of his studies on Mount Shasta 

 (see Merriam. 1899). Further discussion, particularly germane 

 in the present connection, is contributed in Hall's (1902) Botan- 

 ical Survey of San Jacinto Mountain. 



In a broad way the extent of life zones is dependent upon 

 temperature, more particularly of the summer season. San 

 Jacinto Peak rises to a height of 10.800 feet, from a base level 

 on the west side of 1500 feet, and on the east side of less than 

 500 feet. This great increase in altitude brings commensurate 

 but converse modification in temperature, varied locally, however, 

 by a score of subsidiary factors. 



The remarkable abruptness of the declivity on the northeast 

 side of San Jacinto peak results in the crowding of all the zones 

 from Lower Sonoran to Boreal into the extraordinarily narrow 

 air-line distance of three miles. The zones represented on the 

 immediate slopes of the mountain are thus (1) Lower Sonoran, 

 (2) Upper Sonoran, (3) Transition, and (4) Boreal (see plates 

 6 and 7). 



While we thus employ four zone names. Hall (1902) recog- 

 nized five. Hall did not deal specifically with the Lower Sonoran 

 zone, and hence omitted it in his enumeration. On the other 



