THE HEART^ MOUNTAIN OVERTHRUST, WYOMING^ 



D. F. HEWETT 



United States Geological Survey 



CONTENTS 



Summary of Results 



Introduction 



Surface Features 



Stratigraphy 



McCuLLOCK Peak Exposures 



Physical Features oe the Overthrust 



Age oe the Overthrust 



Tertiary Deformation and Sedimentation in the Bighorn Basin 



ILLUSTRATIONS 



Fig. I. — Sketch geologic map of region near Cody, showing Heart Moun- 

 tain overthrust. 



Fig. 2. — Cross-sections of the Heart Mountain overthrust 



Fig. 3. — -The McCuUock Peak region viewed from the southwest, near 

 Cody, Wyoming. 



Fig. 4. — -Bighorn limestone ( ?) overlying Wasatch (or Bridger ?) beds on 

 a hill near East Peak, McCuUock Peak region, near Cody, Wyoming. 



SUMMARY OF RESULTS 



The recognition in 191 9 of blocks of Madison limestone (Missis- 

 sippian) overlying beds of the Bridger epoch (middle Eocene) in 

 the McCullock Peak region, 12 miles east of Cody, Wyoming, shows 

 that the overthrust fault recognized by Dake (2) in 191 6 is much 

 more extensive than first suspected. Dake mapped the fault in a 

 belt 30 miles long, vs^ithin w^hich the extent of overthrust was 

 estimated at 16 miles. He also noted the existence of thrust faults 

 along the east front of Beartooth plateau, where pre-Cambrian 

 rocks overHe "Red Beds" (Chugwater formation) but did not 

 assume continuity with the Heart Mountain overthrust. The 

 residuals on McCullock Peak show that the extent of overthrust 

 is at least 28 miles and indicate that the fault should be traceable 



' This spelling approved by United States Geographic Board, 1909. 



2 Published by permission of the director, United States Geological Survey. 



536 



