No. 3.— Post-Pleistocene Drainage Modifications in the Black Hills 
and Bighorn Mountains. 
By GEORGE ROGERS MANSFIELD. 
CONTENTS. 
PAGE PAGE 
Intröduchome m end Discussion of Literature 
The Problem Outlined . . . 60 Quaternary Lake (?) . . 70 
Methods of Work ee) Question. of Uplite nr 2 CL 
The Black Hills District . . 61 Development of Drainage 74 
The Gravels er Conclusions ah ds i ee 10 
Character and Distribution 61 The Bighorn District elle) 
Sources is e The Gravels o O 
des a ae ey 08 Tavera. ea ee a 
Terraces and Slopes . . . 64 Slopes era peo 
Stream Elbows AD Question of Up... 79 
Bear Butte Creek — Boul- Climatic Oscillation . . 79 
der Parke = wu Oe Crustal Movement . . . 79 
Boulder Park — Crook Drainage Changes . . . . 81 
Valley? mierni 3 mo 2» OF Big Goose Creek... . 82 
Whitewood Creek . . . 67 The Red Canyon . . 83 
Sandy Creek sen. rela 0567 Beheaded Streams . . . 84 
Spiegel's Gap pea Ou Obsequent Gashes . . . 84 
Present Stream Courses . . 68 A Resequent Ril «... . 8 
Summary of Field Evidence 68 Summary ore oO 
Discussion of the Literature 70 Bibliography 0.20.22. .86 
Origin of the Gravels . . 70 Plates 
INTRODUCTION. 
In the summer of 1904 the writer spent five weeks in the Black Hills 
and Bighorn Mountains, as a member of the Harvard Summer School 
of Geology under the direction of Professor T. A. Jaggar, Jr. About 
two weeks were spent in investigations of a general nature, while the 
remaining time was devoted to the study of a special problem in the 
two fields indicated. The portion of the Black Hills studied (Plate 
2) is roughly twelve to fifteen miles in diameter and has for its center 
a point on Boulder Creek about four miles northeast of Deadwood. 
The Bighorn district (Plate 4) occupies the front slope and foot-hills 
of the eastern flank of the mountains, in the immediate vicinity of Big 
Goose Creek and about fifteen miles southwest from Sheridan, Wyo- 
