FOOTHILLS STRUCTURE IN NORTHERN COLORADO 



VICTOR ZIEGLER 



Colorado School of Mines, Golden, Colo. 



OUTLINE 



Introduction 



Structural Features 



The Foothills Monocline 

 Supposed Local Unconformities 

 The Golden Area 



Structural features at Golden 

 Eldridge's "Arch Hypothesis" 

 Comments on the Arch Hypothesis 

 Proposed Alternative Explanation 

 The Boulder Area 

 Minor Structural Features 

 Minor Folds 

 Minor Faults 

 Summary 



The Master-Monocline 

 The Main Faults 

 Conclusion 



INTRODUCTION 



The area under discussion comprises a part of the foothills of the 

 " Front Range " of Colorado, west and north of Denver, and extends 

 from Morrison about 70 miles north to Fort Collins. No attempt 

 will be made to discuss the stratigraphy of this district nor to 

 describe any of the geological formations in detail; only the 

 structural features will be emphasized. 



STRUCTURAL FEATURES 

 THE FOOTHILLS MONOCLINE 



The "master structural feature" of the foothills has been well 

 described by Fenneman 1 in his discussion of the geology of the 

 Boulder district, and also by Eldridge in the monograph on the 



1 U.S. Geol. Survey Bulletin 265, 1905, pp. 41-43. 



715 



