The tectonic geomorphology of the northern Sangre de Cristo Mountains, near Villa Grove, Colorado Item Type text; Thesis-Reproduction (electronic) Authors Peterson, Robert Howard Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 28/09/2021 19:43:16 Link to Item http://hdl.handle.net/10150/557357 THE TECTONIC GEOMORPHOLOGY OF THE NORTHERN SANGRE DE CRISTO MOUNTAINS, NEAR VILLA GROVE, COLORADO by- Robert Howard Peterson A Thesis Submitted to the Faculty of the DEPARTMENT OF GEOSCIENCES In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE In the Graduate College THE UNIVERSITY OF ARIZONA 1 9 7 9 STATEMENT BY AUTHOR This thesis has been submitted in partial fulfillment of re­ quirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judg­ ment the proposed use of the material is in the interests of scholar­ ship. In all other instances, however, permission must be obtained from the author. APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below: W. B. BULL Date Professor of Geosciences TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS......... iv LIST OF TABLES.. .. ......... vi ABSTRACT ........ ......... vlii 1. INTRODUCTION........ 1 2. LOCATION, GEOGRAPHY AND CLIMATE ............. 5 3. PREVIOUS WORK ...................... 8 4. GEOLOGIC SETTING AND HISTORY . ................ 10 Pleistocene Glaciation . ........ 14 5. TECTONIC GEOMORPHOLOGY MODEL .......... 20 ( 6 . CANYON MORPHOLOGY .......... 24 7. ALLUVIAL FAN MORPHOLOGY AND AGE ............. 37 8. CLIMATIC EFFECTS ON THE MORPHOLOGY OF THE ALLUVIAL FANS.. ............... 65 9. MORPHOLOGY OF THE MOUNTAIN FRONT ESCARPMENT ....... 76 10. SUMMARY AND CONCLUSIONS ................. 90 REFERENCES CITED ..................... 95 iii LIST OF ILLUSTRATIONS Figure Page 1= Location Map of the Study Area 2 2. Telephoto Photograph Looking East toward Hot Springs Canyon ....... ........ 3 3. High-altittude Air Photo Showing the Northern Portion of the San. Luis Valley ............... 6 4. Known Significant Earthquakes of Record in Colorado . « 15 5. Seismicity in Colorado ................. 16 6. Air Photo Showing the Drainage Basin of Black Canyon . 19 7. Dominant Stream Processes ........ 25 8. Variation in Vf Ratios along the Length of a Stream . 27 9. Morphology of Class 1 and Class 2 Alluvial Fans .... 39 10. Glaciation in Black Canyon ............... 66 11. Glacial and Present Snow and Tree Line Gradients .... 67 12. Schematic Diagram of the Pattern of Sedimentation during the Paraglacial P e r i o d ................. 72 13. Glacial Time Scale (from Madole, 1976) ......... 74 14. Development of Faceted.Spurs on the Mountain Front (from Hamblin, 1976) ...... ......... 77 15. Old Alluvial Gravels on a Level 5 Faceted Ridge Crest ......... 79 16. Air Photo of Triangular Faceted Ridges Located between Cotton Creek and Maj or Creek Canyons ........ 80 17. Portion of the Valley View Hot Springs 7 V Quadrangle Showing Correlation of Faceted Ridge Crests .... 81 18. Air Photo of the Southern Portion of the Study Area . 85 iv V LIST OF ILLUSTRATIONS— Continued Figure Page 19. Air Photo of the Northern Portion of the Study Area . „ 86 20. Air Photo of the Hot Springs Canyon Fan Showing the Junction of the Villa Grove and Sangre de Cristo Fault Zones .................... 87 21. Seismic Risk Map of the United States ......... 91 22. Tectonic Geomorphology of the Valley View Hot Springs Quadrangle, Colorado ............ In pocket 23. Relationship of Surface Displacement to Earthquake Magnitude ..................... 93 LIST OF TABLES Table Page 1. Glaciation in the Rocky Mountains (after Richmond, 1965) - » . 18 2. Tectonic Geomorphology Model (after Bull, in preparation) ........... 23 3. Canyon Area and Stream Gradients........... 29 4. Vf Ratios . ........................... 31 5. Basin Elongation Ratios . ........ 35 6. Surficial Weathering Characteristics . 43 7. Weathering Characteristics ................ 45 8 . Surficial Weathering Characteristics of the High Steel Canyon Fan ........ '....".......... 48 9. Surficial,Weathering Characteristics of the Low Steel Canyon F a n ............... 49 10. Surficial Weathering Characteristics of the Lime Canyon Fan ......................... 50 11. Surficial Weathering Characteristics of the Black Canyon Fan . ......... 51 12. Surficial Weathering Characteristics of the Orient Canyon Fan ...................... 52 13. Surficial Weathering Characteristics of the High Hot Springs Canyon Fan ............... ........ 53 14. Surficial Weathering Characteristics of the Low Hot Springs Canyon Fan . ................. 54 15. Surficial Weathering Characteristics of the Garner Creek Canyon Fan ........................... 55 16. Surficial Weathering Characteristics of the Major Creek Canyon Fan .................. 56 vi v±i LIST OF TABLES— Continued Table Page 17. Surficial Weathering Characteristics of the High Cotton Creek Canyon Fan ........ .......... 57 18. Surficial Weathering Characteristics of the Low Cotton Creek Canyon Fan ............... 58 19. Alluvial Fan Characteristics ......... ........ 60 20. Comparison of Knepper and Marr's (1971) and Peterson’s (this Study) Classification of Alluvial F a n s ............. 63 21. Processes during Glacial, Paraglacial and Interglacial Time ................................... 75 22. Summary of Faceted Ridge Crest Data 83 ABSTRACT Studies defining the earthquake hazards at the northern end of the San Luis Valley and Sangre de Cristo Mountains of Colorado have classified it as an area of minor seismic hazard, but these studies are limited to the activity recorded during the last 150 years. The area’s tectonic geomorphology allows estimates of Quaternary tectonic activity. The mountain streams are actively downcutting while continuing to depos­ it sediments on the heads of their alluvial fans. For this to occur, the rate of tectonic base-level fall must be greater than the sum of the rates of channel downcutting in the mountains and sedimentation on the alluvial fans. The morphology of the mountain front- escarpment reveals that al­ luvial gravels have been uplifted 130 m above the present valley floor. - This uplift consisted of periods of tectonic quiescence and renewed up­ lift. The most recent evidences of seismic activity found were fault scarps of the Villa Grove and Sangre de Cristo fault zones cutting fan deposits of early Holocene age. Apparently the northern Sangre de Cristo-San Luis Valley is an area of potential future tectonic activity, and classifications based on historic records and present seismicity are inadequate for determining the true seismic hazards of this area. CHAPTER 1 INTRODUCTION The study area is located in south—central Colorado and contains portions of the San Luis Valley and the Sangre de Cristo Mountains (Fig­ ure 1). It has been recognized that the boundary between the San Luis Valley and the Sangre de Cristo Mountains is a fault (Figure 2), but un­ til recently little attention has been paid to the possible earthquake hazards of the area. Historically the area has not experienced a major earthquake, and current seismic records indicate little seismic activity of magnitude 2 or greater (Simon, 1969). These two forms of data have been the most common criteria used to establish the earthquake hazards of a region, but the limitation is their short period of record. In­ deed, evidence in other areas indicates that periods of fault movement may occur with intervals of more than just 100 or 200 years and the lack of any activity during the historic period is not a positive criterion to establish the lack of any future earthquake activity. In order to gain a better understanding of the earthquake hazards of the area, evi­ dence of tectonic activity prior to the period of historic record must be used. In.the Sangre de Cristo Mountains-San Luis Valley area, the knowledge that periods of fault movement may be greater than that of historic record and visible evidence of past faulting has led Glenn Scott (1970, p. Cll) to state "Faults along the west flank of the S a iid a COLORADO j | Area of index U m ap ■ . 10 Miles | CD U.S.Highways 0 State Highways Monte Vista Figure 1. Location Map of the Study Area. 3 Figure 2. Telephoto Photograph Looking East toward Hot Springs Canyon. — Notice just beyond the end of the road the fault scarp cutting across the Hot Springs Canyon fan. Also no­ tice the amount of area above present tree line. Sangre de Cristo Mountains probably present the greatest likelihood of future earthquakes owing to their thousands of feet of pre-Quaternary movement and the lateness of their last movement less than 10,000 years ago." This study will use geomorphic evidence as a source of prehis­ toric information on the tectonic activity of the faults along the west flanks of the Sangre de