404 PEOCEEDINGS OF THE CALIFORNIA MEETING 



Eead in full from manuscript. Remarks were made by Messrs. E. T. 

 Chamberlin, R. S. Holway, and C. F. Tolman, Jr. 



A MEASURE OF ARID EROSION 

 BY CHARLES KEYES 



{Ahst7-act) 



The arid regions of western America are particularly noteworthy because 

 of the fact that throughout their extent there have been during late geologic 

 times prodigious extravasation of lavas. These outpourings of basaltic mag- 

 mas continued, without luiTisual interruptions, from the early Tertiary period 

 to the present epoch. Being largely extruded over soft deposits of great thick- 

 ness and wide extent, both lava streams and lava fields resist in a remarkable 

 way all erosive influences. In the erosion and the general lowering of the 

 country the areas covered by the lava-sheets soon develop into plains which 

 now are elevated greater or less distances above the surrounding general 

 plains surface. These plateau plains constitute one of the most characteristic 

 features of arid landscapes. 



With the geologic age of the underlying rocks and the time of the lava 

 flowing determined, a measure is provided, within very narrow limits of error, 

 for the time elapsed between the appearance of the effusive cap of the plateau 

 plain, when this level was the general plains surface, and the formation of the 

 present plains surface. There are many svich plateau plains on the northern 

 end of the Mexican tableland. In this connection one in particular deserves 

 especial mention. The level of the great Mesa de Maya, in northeastern New 

 Mexico, now 4,000 feet below the crest of the adjoining Rocky Mountains, is 

 3,000 feet above the next lower plain, the Ocate plateau, which latter is 500 

 feet above the broad Las Yegas plain, now constituting the general plains 

 surface of the region. Into the surface of the latter the Canadian River in- 

 trenche.s itself to a depth of 2,000 feet. 



"Under conditions of an arid climate, where water action is almost unknown, 

 the erosive power is believed to be mainly the winds. 



Presented by title in the absence of the author. 



A POSSIBLE CAUSAL MECHANISM FOR HEAVE FAULT-SLIPPING IN THE 

 CALIFORNIA COAST RANGE REGION 



BY HARRY O. WOOD " 



(Abstract) 



The causal mechanism proposed is differential creep of a subcrustal layer, 

 with a maximum movement in the direction of the trend of the Coast Ranges 

 and a minimum transverse to this trend due to lightening of the mountain 

 belts and loading of the valleys and the sea-floor offshore. The principal point 

 in the paper is the hypothesis which explains the causal relation between this 

 transfer of load and the differential creep. 



Presented by title in the absence of the author. 



" Introduced by A. C. Lawson. 



