174 



F. E. PEABODY AND J. M. SAVAGE 



proaching the southern end of the corridor from the interior en- 

 counter a barrier at the southern Sierra crest and at the Transverse 

 Ranges. Warming and drying trends may enable desert species to 

 spread northward into the San Joaquin Valley via Walker, 

 Tehachapi, and Tejon passes. Distribution of the desert night lizard, 

 Xantusia vigilis (Fig. 10), indicates a relatively recent invasion via 

 Tehachapi and up the Sierra foothills, and an invasion via Tejon 



DESERT "** 



/ NIGHT 



jL LIZARD / 



*\ XANTUSIA / 



VIGILIS I 



Fig. 10. Distribution of desert night lizard, Xantusia vigilis. Invasion 

 of foothills on both east and west sides of Great Valley is apparently 

 progressing actively at present. 



and up the dry inner Coast Ranges. A somewhat older invasion 

 through the passes into the San Joaquin Valley is suggested by the 

 distribution pattern of the leopard lizard, Crotaphytus wislizenii 

 (Fig. 11). The San Joaquin subspecies, silus, represents a stock 

 difTerentiated from the parent subspecies of the Great Basin, and 

 certainly reached the San Joaquin Valley from the south, across 

 mountain passes, during a climatic fluctuation. 



Northern elements of the Madro-Tertiary complex have tended 

 to invade the corridor from the north, following the path of Arcto- 

 Tertiary species. The sagebrush lizard, Sceloporus graciosus (Fig. 

 12), has differentiated a Californian subspecies, graciosus, which has, 



