BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 19, pp. 63-92, PL. 5 



May 11, 1908 



EOCK-FLOOE OF INTEEMONT PLAINS OF THE AEID 



EEGION^ 



BY CHARLES E. KEYES 



(Bead before the Society December 30, 1907) 



CONTENTS 



I'age 



Introductory G3 



Foundation of the arid plains 64 



Definition of "bolsou" 64 



Jornada del Muerto as the type ' 65 



Substructure of the Estancia plains 67 



Las Vegas of Nevada 68 



Inter-relationships of iutermont plains of California 69 



Course of the Colorado river 70 



Surface of the Colorado plateau 72 



Bolsons of northern Mexico 72 



Debris of the bolsou plains 73 



Significance of a thinly mantled rock-floor 74 



Origin of the rocli-floor surface 74 



Peneplauation 74 



Planation independent of sealevel 76 



Sheetflood erosion 78 



Eolian erosion in arid regions 81 



I'laya deposits 88 



Arid plains of other regions 85 



Planorasion 86 



Geographic cycle in an arid climate 86 



Recapitulation 91 



Introductory 



The geologic structure of the arid region comprising the Great basin of 

 western America and tlie northern part of the Mexican tableland is sup- 

 posed to be characteristic of that anomalous class of geotectonics known as 

 the Basin Eauge, or Block Mountain, type. Its distinctive feature is 

 commonly considered as the product of normal faulting on a prodigious 



1 Manuscript received by the Secretary of the Society .Tanuary I], 1008. 

 VIII' — Bull. Geol. See. Am., Vol. 19, 1007 



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