182 F. E. PEABODY A\D J. M. SAVAGE 



tions, a derived endemic species {E. lagiinensis) at the tip of Baja 

 California, and a disjunct population in southern Nevada suggest 

 that the species was an early migrant down the corridor. Eumeces 

 gilberti maintains strict separation of range along its western limits 

 except for the sympatry in southern California. There may be a 

 limited sympatry also at the northern end of the range. The species 

 has several disjunct populations in the Great Basin and one in 

 Arizona, all suggesting considerable post- Pleistocene fragmentation. 



The relatively high incidence of sympatry between closely related 

 forms in southern California suggests a set of well-timed physical 

 conditions which must first maintain genetic isolation and then 

 allow the isolation to break down. If the Coast Range corridor, Great 

 Valley, and Sierra block had possessed their present form and rela- 

 tionship from Late Pliocene to Recent, it is doubtful that genetic 

 isolation would have been maintained by west and east arms of 

 species dispersing southward around the Great Valley barrier, 

 whether or not gross climatic changes acted as stimulants. Some- 

 thing must have blocked one of the dispersal routes. The evolution 

 of a Coast Range corridor, as outlined earlier, exactly fulfills the 

 conditions of time, place, and climate necessary to produce the ob- 

 served sympatric conditions. Under the conditions that prevailed, 

 sympatry anywhere else in the far west was unlikely. Also, it was 

 unlikely under prevailing conditions that sympatry would develop 

 in Madro-Tertiary species unless a northern element were to make 

 an end run from the northern Great Basin to the west and down the 

 corridor in company with purely boreal species. That this could 

 happen is indicated by the somewhat special sympatry of the skinks 

 (of example 4, above). Under the prevailing conditions Madro- 

 Tertiary species of more xeric preference could not disperse up the 

 corridor, and in fact, were barred from it until relatively recent 

 times when dispersal over mountain passes has been possible. Fi- 

 nally, it should be emphasized that the areas of sympatric associa- 

 tion are precisely where they should be in relation to the presumed 

 barrier to dispersal down the corridor in Pre-Middle Pleistocene 

 time and to the junction of corridor and Sierran dispersals. (See 

 Fig. 19 for summation.) 



The time when sympatry in southern California became possible 

 must not be earlier than mid-Pleistocene time, if our concept of the 

 evolution of the Coast Range Corridor is correct. Thus one is more 



