478 



GEOLOGY. 



In other localities, the reference of lavas, tuffs, etc., to this period 

 depends on different criteria. In southern California (Mohave desert) 



Fig. 561. — Oven of clots of plastic lava. Jordan Craters, Ore. 

 (Russell, U. S. GeoL Surv.) 



and northern Arizona (vicinity of Flagstaff), for example, there are 

 cinder cones and lava-flows of limited extent which are so slightly 



Fig. 562. — Pressure ridge developed in fresh lavas. Jordan Craters, Ore. 

 (Russell, U. S. GeoL Surv.) 



touched by erosion that there can be little doubt that they date from 

 a time long subsequent to the beginning of the Quaternary period. 



