ANTICLINAL MOUNTAIN RIDGES 167 



comparison of observations must be made that the reader may 

 have the evidence before him. In the second place, this state- 

 ment of the disagreement between the results of earlier recon- 

 naissance and later detailed mapping is important in that it may 

 contribute something in the way of suggestion to the broader 

 problem of determining the origin of the Basin ranges. In the 

 solution of such problems, the observations, largely physiographic 

 in character, made in the course of a rapid reconnaissance, 

 may be found later not to be in accord with the geologic data 

 secured during a careful survey of the same area or a portion of 

 it. The methods employed in reconnoissance work are of neces- 

 sity quite different from those possible in the mapping for folio 

 publication, when a topographic base map is available and the 

 area is thoroughly traversed. Thus, the plea for a rehearing of 

 the evidence does not concern the witnesses so much as the 

 different conditions under which their observations were made. 



The EUensburg quadrangle in central Washington has been 

 mapped geologically by the writer and Mr. Frank C. Calkins, 

 and the results of that survey are incorporated in Folio No. 86 

 of the Geologic Atlas of the United States. The area is one of con- 

 siderable geologic interest, as it lies in the zone intermediate 

 between the Cascade mountains and the Great Plain of the 

 Columbia. It is natural, therefore, that related as this region is 

 to both of these distinct topographic provinces, its geologic 

 study should yield results bearing upon the structure of both 

 the mountains on the west and the plateau on the east. The 

 area is likewise of interest as the one visited earlier by the recon- 

 naissance geologist and as including many localities the descrip- 

 tions of which apparently contain the basis of generalizations 

 concerning the prevalence of the Basin range type in central 

 Washington. In the following pages such descriptions will be 

 cited, followed by comment based upon the results of the later 

 work. For the full discussion of the geology and physiography 

 of this quadrangle the reader must be referred to the EUensburg 

 folio, since the present article can contain only such points as 

 bear directly upon this discussion. 



A brief statement of the geology may serve to introduce the 



