CALIFORNIA PLAINS 



69 



volved, and both these and Paleozoic rocks are standing at high angles, 

 with the tops everywhere evenly beveled. 



INTER-RELATIONSHIPS OF INTERMONT PLAINS OF CALIFORNIA 



Mountain-locked desert plains of southeastern California frequently 

 have their rock-floors covered by only a few feet of soil and debris. 

 Along the Mohave river, northeast of Barstow and elsewhere, artificial 

 excavations have disclosed soft Tertiary strata standing in edge and com- 

 pletely planed off. At the American borax mines, north of Daggett, the 

 following section is shown (figure 4) : 



Figure 4. — Vertical Tertiary Beds, near Daggett, California 



The plain in which the mines are located is very even and without con- 

 spicuous outcrops of bedrock. At the mine shafts the truncated edges of 

 the beds over a considerable area protrude through the thin surface 

 mantle. Similar conditions obtain 10 miles to the northeastward, near 

 the mines belonging to the Pacific Coast Borax Company. 



In other plains of the vicinity the rock-floor appears to be made up of 

 thick andesitic and other lava flows which have been tilted and beveled. 



There is a hypsometric relationship among some of the interment 

 plains of California that is not so apparent anywhere else in western 

 America ; yet similar relations are known to exist in many parts of west- 

 ern and southern Arizona and in New Mexico. The great difference in 

 elevation at which adjoining plains stand above sealevel is very sug- 

 gestive. An east and west profile (figure 5) of the country between the 

 Sierra Nevada and the California-Nevada state line is transverse to the 

 axes of both the valleys and the mountain ranges. Its character suggests 

 frequent and profound faulting; bu.t faulting alone does not appear to 

 offer the full explanation of the unequal altitudes of a given series of 

 desert plains. The question is raised whether there does not exist a more 

 or less perfect independence of neighboring plains in their development, 

 planation, and surface modification under desert influences. The proba- 

 bility of every interment plain in the arid region attaining a level that is 



