This dissertation has been microfilmed exactly as received

WALLACE, Ronald Gary, 1938- TYPES AND RATES OF ALPINE MASS MOVEMENT, WEST EDGE OF BOULDER COUNTY, .

The Ohio State University, Ph.D., 1967 Geology

University Microfilms, Inc., Ann Arbor, Michigan TYPES AND RATES OF ALPINE MASS MOVEMENT, WEST EDGE OF BOULDER COUNTY, COLORADO FRONT RANGE

DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By Ronald Gary Wallace, B.S., M.S.

«****«

The Ohio State University 1967

Approved by

Department of Geology ACKNOWLEDGMENTS

The writer is deeply indebted to Dr. Sidney E. White of the Ohio State University for suggesting this investiga­ tion, for proposing and receiving a National Science Founda­ tion grant to support the project, for his assistance in the field, and for guidance during the writing of this disserta­ tion. An expression of appreciation is also due to Dr. Charles E. Corbato and Dr. Gunter Faure who served as members of the Doctoral reading committee. The writer is also indebted to Dr. George E. Moore, Jr. who read and made suggestions toward improving the dissertation. A statement of indebtedness is made to the National Science Foundation whose support made it possible to carry out the full extent of this three year project. This support included salaries for the writer and a field assistant each year, lodging, food, tents, transportation, photographs, maps, and other equipment. Many thanks are herewith given to the Institute of and Alpine Research of the University of Colorado and to Dr. John W. Marr, Professor of Biology and Director of the Institute, for permission to use and live at the mountain research station near Nederland, Colorado, for the summers of 1964, 1965, and 1966. Lodging, meals, and laboratory facilities were made available. Use of office

ii space, a photographic laboratory, library, and recreation facilities were appreciated. The writer is grateful to the City of Boulder, Colorado, for permission to conduct studies within their watershed property. Field assistants Craig Johnson (1964), James Davis (1965), and Gary Dolezal (1966) are to be thanked for their help during the specified field seasons. Particular appreci­ ation is due to Davis and Dolezal for their excellent photo­ graphic processing of the black and white prints used in this dissertation. Additional thanks are given to Ronald Laughlin, Judith Purley, Richard Bonnett, and James Richards who at various times helped to establish and measure the motion studies. The writer is also indebted to James Benedict, geolo­ gist and research participant at the research station, who was available on numerous occasions for valuable discussions pertaining to problems associated with the writer's field studies.

ill VITA

July 6, 1938 Born, Cadiz, Ohio 1961 .... B.S., Kent State University, Kent, Ohio 1962-1964. . Graduate Teaching Assistant, The Ohio State University, Columbus, Ohio 1964 .... M.S. The Ohio State University, Columbus, Ohio 1964-1967. . Graduate Teaching Assistant, The Ohio State University, Columbus, Ohio 1967 .... Petroleum Geologist, Standard Oil of Texas, Midland, Texas

iv CONTENTS Page ACKNOWLEDGMENTS...... ii VITA ...... iv TABLES ...... ix ILLUSTRATIONS ...... xii PLATES ...... xvll INTRODUCTION...... 1 Purpose of Investigation ...... 1 Location and Boundaries of A r e a ...... 2 Methods of Investigation ...... 2 Previous W o r k ...... 6 GENERAL GEOMORPHIC SETTING ...... 9 Surface Features and Relief ...... 9 Accessibility ...... 10 and Vegetation ...... 11 Introduction ...... 11 Subalpine Region ...... 12 C l i m a t e ...... 12 Vegetation...... 15 Alpine Region ...... 15 C l i m a t e ...... 15 Vegetation...... 17 Drainage...... 17 GEOLOGIC HISTORY ...... 19 Introduction ...... 19 Precambrian to Cenozoic History ...... 19 Precambrian Formations ...... 20 Idaho Springs Formation ...... 21 Swandyke Hornblende Gneiss ...... 23 Boulder Creek Granite ...... 24 Silver Plume Granite ...... 24 Cenozoic History ...... 25 Tertiary Igneous Intrusives ...... 25 Physiographic History ...... 26 Glacial History ...... 29 v CONTENTS (Contd.) Page DESCRIPTIONS OF MASS MOVEMENT FEATURES...... 33 Introduction...... 33 Alpine Processes of ...... 33 G l a c i e r s ...... 37 Introduction ...... 37 Arapaho Rock ...... 39 Location...... 39 Description ...... 39 Evidence of M o t i o n ...... 45 O r i g i n ...... 48 Possible Rock G l a c i e r ...... 54 Arapaho Possible ...... 54 Henderson Possible Rock Glacier ...... 55 Arikaree Possible Rock Glacier ...... 57 Protalus Lobes ...... 59 Introduction ...... 59 Location...... 60 Description...... 61 O r i g i n ...... 66 Examples of Protalus Lobes ...... 71 Blue Lake V a l l e y ...... 72 Isabelle ...... 74 Green Lakes V a l l e y ...... 75 Arapaho Valley ...... 75 Proscree Lobes ...... 77 Introduction ...... 77 Location...... 78 Description ...... 79 Origin ...... 80 Protalus Ramparts ...... 82 Introduction ...... 82 Location...... 82 Description...... 82 Origin...... 83 Scree S h e e t s ...... 84 Introduction ...... 84 Location...... 84 Description ...... 85 Or igin...... 85 Complex Talus Cones ...... 87 Introduction ...... 87 Location...... 87 Description...... 87 Origin...... 89 vi CONTENTS (Contd.) Page Avalanche Boulder Tongues ...... 93 Introduction ...... 93 Location ...... 93 Description ...... 94 O r i g i n ...... 96 Alpine Mudflows ...... 102 Introduction ...... 102 Location...... 102 Description ...... 102 O r i g i n ...... 104 Talus ...... 108 Introduction ...... 108 Location...... 10 8 Description ...... 108 O r i g i n ...... 109 VOLUME AND DISPLACEMENT OP DEBRIS ...... Ill Introduction ...... Ill Procedures...... Ill Blue Lake V a l l e y ...... 116 Motion Study 1 - D ...... 116 Motion Study 1 - C ...... 118 Motion Study 1 - X ...... 120 Motion Study 1 - A ...... 120 Motion Study 1 - B ...... 12 3 Motion Study 1-E ...... 123 Motion Study 2 ...... 125 Isabelle Valley ...... 126 Motion Study 3 - A ...... 126 Motion Study 3 - B ...... 126 Motion Study 3 - C ...... 126 Motion Study 3 - D ...... 126 Motion Study 4 ...... 133 Pawnee Valley ...... 136 Motion Study 5 - A ...... 136 Motion Study 5 - B ...... 139 Green Lakes V a l l e y ...... 141 Motion Study 6 - A ...... 141 Motion Study 6 - B ...... 143 Motion Study 7 ...... 147 Motion Study 8 ...... 148 Motion Study 9 ...... * ...... 151

vii CONTENTS (Contd.) Page Arapaho Valley ...... 152 Motion Study 1 0 ...... 152 Motion Study 1 1 ...... 153 Motion Study 1 2 ...... 157 Motion Study 1 3 ...... 160 Other Examples...... 164 Areas and Volumes of Mass Movement Features .... 164 S u m m a r y ...... 170 DESCRIPTIONS OF GLACIAL FEATURES AND THEIR RELATION TO MASS MOVEMENT F E A T U R E S ...... 172 Introduction ...... 172 Intervalley Glaciation ...... 174 North Fork Middle Boulder Creek Valley ...... 177 Arapaho Valley ...... 178 Henderson Valley ...... 182 N^ve" V a l l e y ...... 184 Green Lakes V a l l e y ...... 184 Isabelle Valley ...... 186 Pawnee Valley ...... 188 Blue Lake V a l l e y ...... 189 Audubon Valley ...... 191 Summary and Conclusions ...... 192 REFERENCES CITED ...... 196

viii TABLES Table Page 1. Records ...... 13 2. Wind Velocities...... 13 3. Air Temperatures ...... 14 *1. Correlation of Stages and Substages in the General Area of Investigation...... 31 5. Dimensions and Volumes of Boulders Involved in Motion Study 1 - D ...... 118 6. Dimensions and Volumes of Boulders Involved in Motion Study 1 - C ...... 120 7. Movement and Volumes of Boulders Involved In Motion Study 1-A, Pig. 3 5 - a ...... 122 8. Dimensions and Volumes of Boulders Involved in Motion Study 1-A, Pig. 3 5 - b ...... 122 9. Dimensions and Volumes of Boulders Involved in Motion Study 1 - B ...... 124 10. Dimensions and Volumes of Boulders Involved In Motion Study 2 ...... 125 11. Movement and Volume ofBoulders Involved in Motion Study 3 - C ...... 131 12. Movement and Volume of Boulders Involved in Motion Study 3 - D ...... 132 13. Dimensions and Volumes of Boulders Involved In Motion Study 4 ...... 136 14. Dimensions and Volumes of Boulders Involved in Motion Study 5-A...... 139 15. Dimensions and Volumes of Boulders Involved in Motion Study 5 - B ...... 139

ix TABLES (Contd.) Table Page - 16. Dimensions and Volumes of Boulders Involved in Motion Study 6-B, line 1 ...... 144 17. Movement and Volume of Boulders Involved in Motion Study 6-B, line 2 ...... 144 18. Movement and Volume of Boulders Involved In Motion Study 6-B, line 3 ...... 145 19. Movement and Volume of Boulders Involved In Motion Study 6-B, line 4 ...... 146 20. Volume of Debris Moved on Motion Study 7 .... 147 21. Movement of Protalus Lobe, Motion Study 6 . . . . 147 22. Movement and Volume of Boulders Involved in Motion Study 8, line 1 ...... 149 23. Movement and Volume of Boulders Involved in Motion Study 8, line 2 ...... 149 24. Movement and Volume of Boulders Involved In Motion Study 8, line 3 ...... 150 25. Dimensions and Volumes of Boulders Involved in Motion Study 9 ...... 151 26. Movement and Volume of Boulders Involved in Motion Study 11, line 1 ...... 154 27. Movement and Volume of Boulders Involved In Motion Study 11, line 2 ...... 155 28. Movement and Volume of Boulders Involved in Motion Study 11, line 3 ...... • 156 29. Movement and Volume of Boulders Involved in Motion Study 12, line 1 ...... 158 30. Movement and Volume of Boulders Involved In Motion Study 12, line 2 ...... 159

x TABLES (Contd.) Table Page 31. Movement and Volume of Boulders Involved in Motion Study 13, line 1 ...... 162 32. Movement and Volume of Boulders Involved in Motion Study 13, line 2 ...... 163 33. Areas and Volumes of Mass M o v e m e n t ...... 166

xi ILLUSTRATIONS Figure Page 1. Relief and drainage map of Boulder County, Colorado ...... 3 2. Map of area of study, Colorado Front Range, Boulder County, showing drainage and locations referred to In t e x t ...... 4 3. Bedrock geology east central portion of Boulder County, Colorado ...... 22 4. Plan view...Arapaho rock glacier at the head of Arapaho Valley ...... 41 Longitudinal profile...Arapaho rock glacier . . . 41 5. View upvalley of Arapaho rock glacier, Arapaho Valley, showing two textural layers ...... 47 6. View of front of Arapaho rock glacier, showing small mudflows and debris that have flowed and slid down the f r o n t ...... 47 7. Buried glacier ice within Arapaho rock glacier . 56 8. Arikaree possible rock glacier, , and Temple Lake moraines at the head of Green Lakes V a l l e y ...... 56 9. Side view of protalus lobe at north base of Kiowa Peak, Green Lakes Valley ...... 62 10. Movement of soil over edge of protalus lobe complex, Isabelle Valley ...... 62 11. Protalus lobe and avalanche boulder tongue, south side of Green Lakes V a l l e y ...... 63 12. Mudflow on and around poorly developed protalus lobe, south side of Green Lakes Valley between lakes #4 and 0 5 ...... 63 13. Mudflow debris resting on snowbank, Green Lakes Valley, summer 1965 ...... 69 xil ILLUSTRATIONS (CONTD.) Figure Page 14. Mudflow debris resting on Ice, Green Lakes Valley, summer 1966 ...... 69 15. Longitudinal cross section showing theoretical forces thought to be necessary in the formation of protalus lobes ...... 71 16. Protalus lobes south side of Blue Lake Valley . . 73 17. Multilobate protalus lobe complex, north of Goose Lake, Arapaho Valley ...... 76 18. Sketch of lobes on protalus lobe complex shown in Figure 1 7 ...... 76 19. Proscree lobes on scree slope north of Mitchell Lake, Blue Lake V a l l e y ...... 81 20. Complex and rockfall talus cones south side Isabelle Valley ...... 90 21. Complex talus cone south side Arapaho Valley showing mudflow l e v e e s ...... 91 22. Detailed map of complex talus cone shown in Figure 2 1 ...... 92 23* Avalanche boulder tongue, north side Arapaho V a l l e y ...... 98 24. Detailed map of avalanche boulder tongue, north side of Arapaho V a l l e y ...... 99 25. Avalanche boulder tongue, north side Blue Lake Valley showing concave surface and spreading t o e ...... 100 26. Avalanche boulder tongue, north side Blue Lake Valley, showing large source area for accumu­ lation of debris and s n o w ...... 100 27. Avalanche boulder tongue, north side Blue Lake Valley showing low angle of toe and the scattering of debris ...... 101 xiii ILLUSTRATIONS (Contd.) Figure Page 28. (A) mudflow with some boulder avalanche debris, (B) mudflow, (C) boulder avalanche with some mudflow debris, south side Arapaho Valley south ofArapaho rock glacier...... 107 29* Mudflow south side of Green Lakes Valley showing fine fluid material at distal end of flow . . . 107 30. Triangular grid showing results of movement of boulders on front of protalus lobe complex 1-D...... 116 31. Protalus lobe complex and talus, south side Blue Lake Valley, south of BlueLa k e ...... 117 32. Triangular grid showing results of movement of boulders on front of protalus lobe 1-C .... 119 33. Photo (August, 1965) of painted debris on front of upvalley lobe of protalus lobe complex south side of Blue Lake V a l l e y ...... 121 34. Results of debris movement of (1) painted line and (2) triangular grid constructed across complex talus 1 - A ...... 121 35. Triangular grid showing results of movement of bounders on complex talus 1 - B ...... 12 3 36. Triangular grid showing results of movement of boulders on rockfall talus 1-E, Figure 31 . . * 12A 37. Triangular grid showing results of movement of boulders on rockfall talus 2 ...... 125 38. Triangular grid showing results of movement of boulders on protalus lobe 3 - A ...... 127 39. Triangular grid showing results of movement of boulders on front of protalus lobe 3-B .... 128 40. Protalus lobe complex and talus, south side Isabelle Valley ...... 129 xiv ILLUSTRATIONS (Contd.) Figure Page 41. Results of motion study based on line painted across complex talus 3 - C ...... 130 42. Results of motion study based on line painted across complex talus 3-D 130 43* Triangular grid showing movement of rock debris at motion study on complex talus cone 4 . . . . 133 44. Complex talus cone north side of Isabelle Valley. 134 45. Detailed map of complex talus cone shown in Figure 4 4 ...... 135 46. Triangular grid showing results of movement of boulders on front of protalus lobe 5-A .... 137 47. Protalus lobes, north side of Pawnee Valley . . . 138 48. Triangular grid showing results of movement of boulders on protalus lobe 5 - B ...... 140 49. Motion study constructed on front of bilobate protalus lobe south side of Green Lakes Valley south of Green Lake No. 5 ...... 141 50. Protalus lobe, Green Lakes Valley, south of Green Lake No. 5 1^2 51. Rockfall talus cones south side Green Lake Valley and Green Lake No. 5 ...... 142 52. Relative positions of rock debris that has moved onto or away from lines painted across complex talus 6 - B ...... 143 53. Relative positions of rock debris that moved onto or away from lines painted across rockfall talus cone 8 ...... 148 54. Movement of debris shown by a triangular grid constructed across rockfall talus 9 ...... 151 55. Motion study 10 constructed on Arapaho rock glacier at the head of ArapahoVa l l e y ...... 152 xv ILLUSTRATIONS (Contd.) Figure Page 56. Relative positions of rock debris that moved onto or away from lines painted across complex talus 1 1 ...... 153 57* Relative positions of rock debris that moved onto or away from lines painted across complex talus 1 2 ...... 157 58. Talus along south side of Arapaho Valley .... 160 59. Relative positions of rock debris that moved onto or away from lines painted across complex talus 1 3 ...... 161 60. View of the west perpendicular to the north-south trend of the Colorado Front R a n g e ...... 176 61. Pitted surface boulders on till on the floor of Henderson Valley...... 183

xvi PLATES

Map of Mass Movement and Glacial Features of the upper Drainage Areas of South St. Vrain Creek, North Boulder Creek and North Fork Middle Boulder Creek, Boulder, County Colorado ...... (in pocket)

xvii INTRODUCTION

Purpose of Investigation In this dissertation are discussed the results of an investigation of the geomorphic features produced mainly by mass movement in the upper reaches of Boulder Creek and South St. Vrain Creek in Boulder County, Colorado (Figs. 1 and 2). The purpose of the investigation is (1) to study and describe the types of mass movement in this alpine region; (2) to attempt a study of the rates and volumes of debris moved on certain selected mass movement features; (3) to determine as nearly as possible relative ages of the mass movement features and (4) to describe the late glacial features at the heads of these valleys, especially the Neoglaciation moraines, and relate them to the mass movement features. Types of mass movement features described and measured are rock , protalus lobes, proscree lobes, protalus ramparts, scree sheets, complex talus cones, avalanche boulder tongues, alpine mudflows, and rockfall talus. Although rates of mass movement over periods up to two full calendar years have been obtained, they represent only the beginning of what should be an extensive study, conducted over a much longer period of time than was available in the present investigation. Permanent reference points were 2 established in order that the investigation might be continued. Rates and volumes of debris movement over a ten year period might produce quite different results from those obtained for the one and two year periods represented here.

Location and Boundaries of the Area The area and features described in this Investigation are on the east side of the Continental Divide at the west edge of Boulder County, Colorado, and about 30 miles west of the city of Boulder. It is nearly 8 miles north of Nederland and 3 miles west of Ward (Pigs. 1 and 2). It is bounded roughly by meridians 105° 30* and 105° 40' west longitude and by parallels 40° 00' and 40° 06 f north latitude. The area outlined in Figures 1 and 2 is the general area of study. Field investigations were confined mainly to the head­ water regions of North Boulder Creek and South St. Vrain Creek. A very small part of the area is in the upper reaches of North Middle Boulder Creek. The major portion of the investigation was restricted to Arapaho Valley, Green Lakes Valley, Isabelle Valley, and Blue Lake Valley. Tributary valleys to these main valleys are were included.

Methods of Investigation Field work was conducted during July and August of 1964, 1965, and 1966. The main goal of this investigation is two­ fold; (1) to describe and map the mass movement and glacial features, and (2) to determine the rates and volumes of debris Pig. 1.--Relief and drainage map of Boulder County, Colorado. Area enclosed in red is the approximate area of study. 4

Fig. 2.— Map of area of study, enclosed in red, Colorado Front Range, Bouider County, showing drainage and locations referred to in the text. C-l, D-l, D-4, and S-l indicate the locations of weather stations referred to in Tables 1, 2, and 3. Short dashed lines show roads passable by motor vehicle. 105 40 13221 Mt Audubon

112979 M itchell lo lc e — toke- 1294 J Paw nee1

Pawi

Valle Long lake la k e Isabelle

Bald Mtn N i wo t d ge IMS!

N avajo

13101 Kiowa

A lbion Mt Albion C r e e k 12596

Lo^°

N ™ 06 L Goose * Arapaho nr Lake Island Silver Lake ci V ^ Pk / Henderson la k e ) Arapaho l$ X k)r G la cier

[ ^PlakeQ._ /y Fourth of July Mine \D o r o th y

3 m ile s

D ia m o n d Lake moved on selected mass movement features. Because of the nature of this goal, numerous methods were used in an attempt to determine rates and volumes of debris moved. Wherever possible, aerial photographs were used for a preliminary investigation. Aerial photographs were especi­ ally useful in locating glacial and mass movement forms. Morainal relationships within and between valleys were identified more easily by aerial photographs. Forms of mass movement could be detected on photographs, although the smaller distinguishing features were not evident. The forms of mass movement are complex talus cones, protalus lobes, rock glaciers, rockfall talus, avalanche boulder tongues, scree slopes, proscree lobes, mudflows, and protalus ramparts. Ridge patterns on the rock glaciers and protalus lobes, which were caused by differential movement, were easily detected on aerial photographs. Descriptions of the forms mentioned above and the finer distinguishing features were obtained by direct field observations. Glacial and mass movement features were mapped on photographically enlarged 7*5 minute U. S. G. S. topographic maps (Plate I). Distances of movement and volumes of debris were deter­ mined entirely by field observations. Flow ridges on aerial photographs display relative rates and directions of movement but absolute rates of movement were not attempted by a photographic study. Depending on the location and size of the mass movement features, a number of methods were used to 6 determine the distances of movement and volumes of debris moved. Descriptions of the methods used are outlined in the chapter concerned with distances and volumes of mass movement debris moved. Approximately four days of fieldwork were used during the early part of the 1964 field season to study rock glaciers in the of southern Colorado. Pierson Basin and Silver Basin near Ouray, Colorado, contain what could be termed ‘’text book” examples of rock glaciers. The rock glaciers in that area are more numerous and better developed than those in the area of investigation. The pur­ pose of this brief study was to see examples of well- developed rock glaciers and to compare them with those in Boulder County, Colorado.

Previous Work One of the earliest investigations of the eastern part of Boulder County, Colorado, was by Thornbury (192 8), who studied the glaciation along the east side of the Colorado Front Range between and . Wahlstrom (1940) investigated the Audubon-Albion monzonite stock that intruded Precambrian rocks between Mount Albion and Mount Audubon. In connection with this Investigation he mapped till undifferentiated in Blue Lake, Isabelle, and Green Lakes Valleys. Wahlstrom (1947) described the Cenozoic physiographic history of the Colorado Front Range and pre­ sented a concise description of older till on Niwot Ridge and 7 Mount Albion. Ives (1953a) also published on the Nlwot Ridge till. Madole (I960 and 1963) reported on the Quaternary geology of the St. Vrain drainage basin, which includes Blue Lake and Isabelle Valleys. He described and mapped Niwot Ridge Till, Wisconsin and Neoglaciation glacial features, and numerous mass movement features. Ives (1953b) published on late glaciation in Silver Lake Valley (Arapaho Valley in this dissertation) and on glaciation in the lower portion of Green Lakes Valley. He did not, however, mention the glacial features in the upper part of Arapaho Valley. Lovering and Goddard (1950) published on the geology and ore deposits of the Front Range, and included with their publication a geologic map of Front Range. Figure 3 is derived from Lovering and Goddard’s geologic map. Very little geologic work has been done on mass move­ ment features in this part of the Colorado Front Range. Ives (19*10) described, photographed, and postulated possible origins for rock glaciers in the Front Range. His study did not include Arapaho rock glacier, the only distinctive rock glacier In the area of investigation. White (1965) published a brief description of Arapaho rock glacier. Outcalt and Benedict (1965), by photo-interpretation, described two types of rock glaciers in the Front Range. Benedict is presently studying types of patterned ground and the associated move­ ment of debris due to freezing and thawing on Niwot Ridge. In 1966 he obtained radiocarbon dates from organic material burled beneath a stone-banked terrace on Niwot Ridge. Through this study he was able to determine periods of maximum move­ ment of sollfluction debris. Waldrop (1964), through field observations and the compiling of previous data, was able to compile a 60 year record of the activities of Arapaho glacier. This work was carried further by Outcalt and MacPhail (1965) in a survey of Neoglaciation in the Colorado Front Range. Marr (1961) has done considerable work on the ecosys­ tems in this part of the Colorado Front Range. Ives (1953b), Marr (1961), and Paddock (1964) have compiled records of temperature, moisture, and wind velocities pertaining to the area of investigation. GENERAL GEOMORPHIC SETTING

Surface Features and Relief Surface features and relief are shown in the area outlined in Figures 1 and 2, and Plate I. Maximum relief in the area is approximately 3,262 feet attained in Arapaho Valley. Relief in the remaining valleys is as follows: North Fork Middle Boulder Creek Valley, 2,534 feet; Green Lakes Valley, 2,809 feet; Isabelle Valley, 2,888 feet; and Blue Lake Valley, 2,488 feet. The major portion of the relief and surface features is the result, either directly or indirectly, of glacial sculpturing. This has resulted in rugged mountainous terrain. Glaciation has carved U-shaped valleys which trend eastward from the Continental Divide. Several of the major U-shaped valleys contain glaciated tributary valleys. Examples are Henderson and Ne've' Valleys, both tributaries to Arapaho Valley; Pawnee Valley, a tribu­ tary of Isabelle Valley; and Audubon Valley, a tributary of Blue Lake Valley (Fig. 2). Each of the five major valleys is a. multi-cirque valley containing at least two cirques. These valleys, containing glacial features such as end moraines, ground moraine, and riegels, provide the setting for mass movement features on which the bulk of the present investiga­ tion has been concentrated. 9 10 Longitudinal profiles of the major valleys show con­ siderable variation. Arapaho Valley has little relief east of Triple Lakes. Upvalley and west from these lakes the valley floor is very steep with numerous high bedrock riegels. Here the valley floor is level for no more than a few hundred feet. Green Lakes Valley is characterized by a multi-stepped profile where bedrock riegels are numerous. Lakes are present between steps. This valley profile shows the greatest number of bedrock steps. The profile of Isabelle Valley shows a series of steps less pronounced than those In Arapaho and Green Lakes Valleys. Lake Isabelle Is on the most distinctive step. Blue Lake Valley is characterized by the smoothest profile; bedrock steps are present but their relief is minor In comparison to those of the other valleys. High flat areas are common between valleys (Fig. 60). These areas, described later in more detail, are considered by some investigators as remnants of a former erosion surface, the Flattop peneplain (Wahlstrom, 19*17). Portions of this surface are thought to be covered by pre-Wisconsin till.

Accessibility Lower portions of the valleys are all accessible by highway. A paved road extends to within one mile east of Mitchell Lake in Blue Lake Valley and one-quarter mile east of Long Lake in Isabelle Valley. The upper portions of these two valleys are reached by foot-tralls maintained by the U.S. Forest Service. 11 Green Lakes Valley and Arapaho Valley, both within the City of Boulder Watershed, are accessible by gravel and dirt roads. Permission to use these roads and to enter the water­ shed must be obtained from watershed authorities. The roads extend as far upvalley as Green Lake No. 3 in Green Lakes Valley and to Goose Lake in Arapaho Valley (Fig. 2). Trails in these two valleys are poor and have not been maintained since the establishment of this area as a private watershed. The lower portion of the North Fork Middle Boulder Creek Valley is reached by a gravel road which leads to the Fourth of July Campground. A well-maintained trail leads from the campground to Arapaho Pass at 11,960 feet and Arapaho Saddle at 12,680 feet (Plate I). Although the valleys are all easily accessible, much time is involved in driving and especially hiking to reach their upper portions. Walking distances range from two to four miles and in most cases, portions of the grade are steep.

Climate and Vegetation Introduction This portion of the Colorado Front Range is restricted almost entirely to the subalpine and alpine climatic and vegetational zones. Many local variations of climate, both macro- and are present in each zone. Only the subalpine and alpine zones will be discussed here. Alpine and upper subalpine zones are more important. The division between the two zones is '‘timberline" or "treeline" (Marr, 12 1961). Most of the climatic and vegetational information, except where otherwise designated, is from Marr (1961). Climatic data compiled in Tables 1, 2, and 3 is de­ rived mainly from Ives (1953b), Marr (1961), and Paddock (1964). The locations of stations C-l, S-l, D-l, and D-4 at which temperature, wind velocity, and precipitation were recorded are shown in Figure 2. Station C-l (10,000 feet) is on a subalpine ridge, S-l (10,200 feet) is in a subalpine valley, D-l (12,300 feet) Is on an alpine ridge, and D-4 (11,600 feet) is in an alpine valley.

Subalpine Region Climate: The subalpine region lies approximately between the elevations of 9,300 and 11,000 feet and cuts across the lower­ most of the conspicuous glacial cirques. This climatic zone is represented In Tables 1, 2, and 3 by the C-l station at 10,000 feet and the Silver Lake station (S-l) at 10,200 feet. Station C-l Is near the east end of the Niwot Ridge but off the southeast end, whereas the Silver Lake station is In Arapaho Valley near Silver Lake (Fig. 2). Summers in the subalpine region are usually short, cool, and moist. Late snow banks and frequent thunder storms account for the high moisture. Autumn is usually dry with cool days and cold nights. Early snows are common in late August and early September. Numerous intervals of clear, calm, hot days and cool nights are common. Winters are long, cold, and windy. Normally an abundance of snowfall and TABLE 1. Precipitation Records

Station No. Precipitation In inches of water Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Annual C-l 1.6 1.6 2.2 3.3 3.6 2.1 2.6 2.3 1.9 1.2 1.6 1.5 25.6 S-l 2.3 2.8 3.5 4.5 2.6 2.4 3.6 2.3 2.4 1.9 1.3 1.9 31-3 D-l 1.9 1.7 2.2 2.3 2.8 1.9 2.9 2.6 1.8 1.2 1.6 1.6 24.6 D-4 3.2 2.8 3.3 3.4 4.3 2.8 2.9 3.7 .7 .4 2.3 2.3 32.8 After Ives (1953b), Paddock (196*1), and Marr (1961). C-l and D-l repre­ sents a 7 year record from 1953-1960. The Silver Lake (S-l) record is a 32 year average. D-4 is a 1 year record. See Pig. 1 for station locations.

TABLE 2. Wind Velocities (mph). (Oct. 1952-Oct. 1953)

Station No. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Annual

C-l 22 15 13 9 8 7 6 6 8 8 9 15 10 D-l 30 25 22 20 14 12 9 11 15 17 22 24 19 D-4 28 22 18 18 11 9 9 11 14 16 19 20 16 After Marr (1961, pp. 127, 131, 134). See Pig. 1 for station locations. TABLE 3* Air Temperatures (°P) (Oct. 1952-Oct. 1953)

Station No. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Max 44 40 54 56 59 75 74 71 68 62 51 48 Min -7 -10 1 2 6 29 35 33 25 12 -10 -14 C-l Mean Daily Max 29 25 34 36 43 63 67 65 62 53 30 27 Mean Daily Min 16 8 16 18 25 38 44 41 36 28 12 13 Max 32 24 41 47 46 61 62 57 57 50 32 34 Min -3 -15 -9 -4 5 25 35 32 23 9 -18 -10 D-l Mean Daily Max 18 13 21 23 32 51 55 51 59 51 18 15 Mean Daily Min 8 1 9 11 19 36 41 37 34 27 7 5 Max 32 27 42 48 52 62 65 60 57 54 34 36 Min -1 -14 -7 -1 4 27 36 35 26 12 -15 -14 D-4 Mean Daily Max 20 15 23 26 36 52 57 53 51 43 21 17 Mean Daily Min 10 3 11 13 20 37 43 40 35 29 .8 6 After Marr (I960, pp. 127, 131, 134). 15 accumulation occurs. Spring is short, cool, and wet. A snowfall of 2 or more feet occurs nearly every spring. Vegetation: According to Marr (1961, p. 55), the most homogeneous, simple, and continuous vegetation types of the Front Range occur at intermediate altitudes in the subalpine region. A dense evergreen forest of spire-crowned spruce and fir trees comprise this zone. In contrast, the upper part of the subalpine is heterogeneous. This difference is due mainly to variations in soil parent material, topography, and patterns of heavy snow accumulation. It is the upper limit of this area that forms the timberline. On the higher dry windswept slopes, the dominant species is twisted and gnarled limber pine. Subalpine fir and Engelmann spruce are the most frequent species In the high valley bottoms and on sheltered slopes.

Alpine Region Climate: The alpine region lies between timberline and the mountain peaks. This region is characterized In the upper portion of the valleys and the higher interstream divides. Most of the climatic data was obtained from the D-l station on Niwot Ridge and the D-4 station at Green Lake No. 4 In Green Lakes Valley (Fig. 2). The alpine- summer is very short and cool to cold. Thunderstorms are frequent and are commonly accompanied by sleet and hail. Rains are often cyclic, occurring at the 16 same hour each day for as much as two weeks at a time. During the summer of 1965, a two week period was character­ ized by thunderstorms at 2:00 p.m. every day, while in 1966 a similar period had storms at 5:00 p.m. Rain is usually sporadic, occurring in some valleys and not in others. Year to year precipitation shows considerable variation; for example, the summer of 1964 was considered to have a rather normal amount of rain resulting in favorable trail, road, and working conditions; the summer of 1965 was extremely wet resulting in wet trails, roads, and the loss of numerous days in the field; the summer of 1966 was unusually dry causing ideal trail, road, and working conditions early in the field season (early June). Autumn is usually short, clear, dry, and cold. Some warm days occur during Indian summer. Win­ ters are not exceptionally cold (-25°F is a 9-year absolute minimum), but they are long and very windy (Osburn et al., 1965, p. 21). Blizzards are frequent and severe. Due to the high wind, very little snow is added to the higher tundra areas. Snow is quickly blown into ravines, into valleys, and into the upper forested regions. The strong westerly winds account for the accumulation of snow in the cirques In sheltered lee areas. Spring is short, cool, and wet. It is characterized by heavy wet snowstorms and by reduced winds. 17 Vegetation: Perennial sedges, grasses, herbs, and minute shrubs dominate the alpine-tundra vegetation. There is an absence of upright trees and tall shrubs. Higher ridges show only a dry meadow association of , xerophytic grasses, and sedges. Above timberline the valleys are characterized by a mixture of xerophytic, mesophytic, and wet meadow plants. Lichens are the dominant form of plant life in the cirque areas. Snow fields and large drifts influence the vegetation because they dictate the length of the growing season. Congeliturbation, solifluction, and depth and duration of snow cover play an important part in controlling the charac­ teristics of the vegetation.

Drainage Drainage in this part of the Front Range is separated into two drainage basins, the St. Vrain Creek basin and the Boulder Creek basin. Niwot Ridge serves as the drainage divide (Figs. 1 and 2). Blue Lake Valley and Isabelle Valley are both in the St. Vrain basin. They are drained by South St. Vrain Creek and its headwater tributaries. This creek flows east, then north into St. Vrain Creek and emerges from the mountains east of Lyons, Colorado (Fig. 1). Green Lakes Valley, Arapaho Valley, and North Fork Middle Boulder Creek Valley are all part of the Boulder Creek basin. Green Lakes and Arapaho Valleys are drained by North Boulder Creek. 18 North Pork Middle Boulder Creek Valley is drained by North Fork Middle Boulder Creek. Both of these creeks drain into Middle Boulder Creek which emerges from the mountains at Boulder, Colorado. The overall drainage pattern in the two drainage sys­ tems is dendritic (Pig. 2). The drainage is to the east away from the Continental Divide and toward the Great Plains. Numerous glacial lakes are present in the upper tributaries of the two drainage basins. GEOLOGIC HISTORY

Introduction Following is a brief outline of the geologic history of that portion of the Colorado Front Range covered in this investigation. The purpose here is to offer a general but rather complete account of major geologic events that occurred prior to late Pleistocene. Events of late Pleistocene and Recent, essentially Neoglaciation time, are the main subject of this investigation.

Precambrian to Cenozolc History Much of the exposed Precambrian rocks of the Colorado Front Range consists of intensely metamorphosed steeply tilted rocks, of sedimentary origin. Within these meta- morphic rocks are large masses of acidic plutonic rocks. Some of the metamorphic rocks have been so changed it is dif­ ficult to decipher their original character. The Precambrian history is very difficult to inter­ pret and will not be attempted here. In general, the present metamorphic grade or mineral composition of the Precambrian rocks composing the core of the Colorado Front Range was attained during the Precambrian period. These rocks were beveled prior to the deposition of the first Paleozoic rocks.

19 20 The area remained a stable continental platform until late Mississippian time when the Front Range geanticline was formed. Beginning in late Mississippian and continuing through Pennsylvanian and into Permian times, the initial structures and trends of the Colorado Front Range were formed. These later Paleozoic structures are obscure due to deforma­ tion during the Laramide orogeny. By early Mesozoic time, crustal activity had largely ceased, and the topography was reduced to low relief. It is postulated that the entire Precambrian core, which had been raised during the formation of the Front Range geanticline, was covered by Triasslc, Jurassic, and Cretaceous (King, 1959). Despite the deposition of these sediments over the eroded geanticline, the area remained a zone of weak­ ness. In late Mesozoic time, crustal forces again came into prominence and the Cordilleran deformation began, which resulted in uplift and removal of the entire sedimentary cover from this portion of the Front Range. Paleozoic and Mesoeolc formations are present in intermontane basins and in the Great Plains. Within these formations lie the details that record the events of the formation of the Colorado Front Range.

Precambrian Formations Basement rocks of the Front Range are Precambrian and range in age from 1800 to 900 million years B.P. (Knight, 196*1, P* !)• In the area of investigation, the only rocks 21 younger than Precambrian are those associated with the Audubon-Albion stock of early Eocene or possibly Paleocene age (Wahlstrom, 1940, P* 1790). The bedrock geology is shown in Figure 3. Precambrian formations from oldest to youngest are the Idaho Springs formation, the Swandyke hornblende gneiss, the Boulder Creek granite, and the Silver Plume granite (Fig. 3). These metamorphic and plutonic rocks are important because they serve as indicators in the glacial till. Madole (I960 and 1963) found the different rock types especially useful in detecting early Wisconsin and pre- Wisconsin glacial deposits that lie beyond the limit of late Wisconsin glaciation.

Idaho Springs Formation: Gneisses and schists of the Idaho Springs formation constitute the oldest rocks in the region. They are foliated, highly metamorphosed rocks largely derived from a thick series of early Precambrian conglomerate, ­ stone, shale, and Impure (Wahlstrom, 1940), p. 1793). According to Lovering and Goddard (1950, p. 19), quartz- biotite schist and quartz-biotite-sillimanite schist are most common. Quartzite and quartz schist and gneiss are common locally. According to Wahlstrom (1940, p. 1973), biotite- sillimanite gneiss is dominant, with smaller amounts of garnetiferous gneiss, pyroxene gneiss, amphibolite, and quartzite. The Idaho Springs formation may best be described as a schist that has been impregnated with granitic material. 22

-40

fir-

Pig. 3.— Bedrock geology, east-central portion of Boulder County, Colorado (Lovering and Goddard, 1950). EXPLANATION

Quaternary Till and alluvial deposits

Tertiary Audubon- Albion stock

Silver Plume granite

Boulder Creek granite Precambrian )

Swandyke hornblende gneiss

□ Idaho Springs formation 23 The Idaho Springs formation forms the main rock type of the upvalley portions of both Arapaho and Green Lakes Valleys. The present cirques have developed almost com­ pletely within this formation (Fig. 3). The formation is faulted and highly jointed, both of which are contributing factors in the supply of debris to existing periglacial deposits.

Swandyke hornblende gneiss: According to Lovering and Goddard (1950, p. 20), the Swandyke hornblende gneiss is com­ posed chiefly of alternating light and dark gray layers of hornblende gneiss generally interlayered with thin units of quartz-biotite schist. Certain portions of this formation are similar to hornblendite, as they show almost no gneissic structure. The more gneissic portions are similar in appear­ ance to the Idaho Springs formation. The uppermost part of the Arapaho cirque contains the only outcrops of the Swandyke hornblende gneiss in the area. The Continental Divide closely follows the outcrop of this formation. The shape is elongated and dike-like. Glaciation in the Arapaho cirque has eroded completely through the elongated structure near the divide. Large blocks of Swandyke hornblende gneiss are present in the Arapaho rock glacier. Many large blocks consisting mainly of hornblende have been weathered and now form piles of rubble on the rock glacier. The hornblende appears to be highly susceptible to . 24 Boulder Creek granite: The Boulder Creek granite is the oldest major Intrusive in the area. The word granite is in part a misnomer. Wahlstrom (1940, p. 1793) uses the term Boulder Creek gneiss and he states that petrographically it is a granodiorite. Lovering and Goddard (1950, p. 25) refer to this rock as the Boulder Creek granite. They say the formation commonly ranges in composition from a quartz monzonite to a sodic granite but that it is predominantly a coarse-grained primary gneiss. From personal observations, it appears that granite, quartz monzonite, and gneiss are all common. Wahlstrom (1940, p. 1794) maintains that the contact between the Boulder Creek granite and the Idaho Springs forma­ tion is everywhere conformable. Boulder Creek granite extends from south of Arapaho Valley north into Green Lakes Valley. A tongue-like projec­ tion of the granite is present between Mt. Albion and Kiowa Peak, which may provide some bedrock control here in produc­ ing a peneplain-like surface between the two peaks.

Silver Plume granite: The Silver Plume granite constitutes the youngest major Precambrian rock unit in the Front Range. Wahlstrom (1940, p. 1795) defines the Silver Plume granite as consisting of nearly equidimenslonal grains of quartz, tablets of orthoclase and microcline, with minor amounts of biotite. The texture varies from medium to coarse. Typically the Silver Plume granite is porphyritic. Potassium feldspar crystals (orthoclase and microcline) form the phenocrysts. A 25 striking feature of this rock is the parallel and subparallel alignment of the prismatic crystals of potassium feldspar. Feldspar phenocrysts appear to be the most resistant mineral in the rock and as a result occur projected on the weathered surfaces of Silver Plume boulders. This distinctive weather­ ing feature will be used later as a possible means for determining the age of till. The Silver Plume granite here is restricted mainly to Isabelle and Blue Lake Valleys. The granite in this area has been intruded by the Audubon-Albion stock, composed largely of monzonite. The stock is early Eocene or possibly Paleocene in age (Wahlstrom, 19^0, p. 1790).

Cenozolc History Terltary Igneous Intrusions Teritary igneous rocks are present as stocks in a belt extending from Jamestown, in Boulder County, diagonally south­ west across the Front Range to Montezuma, in Summit County. Most of the stocks appear to have been emplaced a short time after the initiation of the Laramide uplift. The larger stocks are of Paleocene and Early Eocene age (Wahlstrom, 19^7, p. 556). Flows and pyroclastic rocks of probable mid-Tertiary age occur in the western part of Rocky Mountain, National Park; , a dissected , Is an example. The positions of the related flows and pyroclastic material have 26 been used by Wahlstrom to place time values on certain events of the physiographic history of the Front Range. The Tertiary rocks within the area of study are of intrusive origin. They belong to the Audubon-Albion stock. The stock extends from Mt. Audubon, across Blue Lake Valley, Isabelle Valley, Niwot Ridge, and south of the old mining town of Albion in Green Lakes Valley (Fig. 3)* A small isolated extension is present south of Island Lake in Arapaho Valley. The stock Is a composite monzonite intrusive which cuts across all the older rocks. The sequence, from oldest to youngest, is syenogabbro, monzonite, quartz-bearing monzonite, syenite, and granite (Wahlstrom, 19^0, P- 1790). Wahlstrom believes that considerable periods of time elapsed between the successive periods of injection, because each phase of the stock was chilled against an earlier phase.

Physiographic History The various surfaces of erosion in the Front Range have long been a subject of controversy. Numerous surfaces at different elevations are present; many of them are small and Isolated. It Is the so-called correlations of these surfaces that has caused different interpretations of the physiographic history of the Front Range. The main problem is whether the different surface levels represent different erosional periods or only one or two erosional surfaces owing their different altitudes to faulting and differential warping. 27 Within the boundary limits of this dissertation, numerous flat, smooth, or gently sloping surfaces at various levels occur (Fig. 60). The more notable surfaces are as follows: (1) a flat but sloping surface between Mt. Albion and Kiowa Peak, which rises to the west toward the Continen­ tal Divide; (2) a smooth but somewhat sloping and irregular surface east of Mt. Albion on the divide between Green Lakes Valley and Arapaho Valley; (3) Niwot Ridge; (4) a small but distinct surface north and above Isabelle Lake; (5) a small flat surface at Pawnee Pass; (6) a number of closely spaced levels on the ridge between Isabelle Valley and Blue Lake Valley; and (7) a distinct east-sloping surface on the east flank of Mt. Audubon. These surfaces will be discussed later in association with pre-Wisconsin till that is thought to cover some of them. Davis (1911, pp. 44-47) was probably the first to describe the physiography of the Front Range. He regarded the summits as being accordant and as remnants of a differ­ entially upwarped peneplain. He referred to this peneplain as the "Highland peneplain of the Front Range." W. T. Lee (192 3) was the first to use the terms Flat- top peneplain and Rocky Mountain peneplain. He named the Flattop peneplain after the Flattop Mountain area in Rocky Mountain National Park, where a number of accordant levels are present at 12,500 feet, which is about the altitudes of Pawnee Pass and Niwot Ridge. Lee considered the Rocky 28 Mountain peneplain to be represented by the flat valley floors cut into the Flattop peneplain and the summits of the foothills away from the higher surfaces. The altitude of this peneplain, according to Lee, ranges from 8,000 to 10,000 feet. Van Tuyl and Lovering (1935) claimed that they could recognize at least five and perhaps eight peneplains. Numer­ ous other workers have expressed their ideas as to the number of erosional surfaces in the Front Range. It is now fairly well accepted that there are two erosional levels in the Front Range, the level of the Flattop surface and the level of the Rocky Mountain surface. The problem is the age or ages of these two surfaces. Were the two surfaces formed at different times or were they originally a single surface that has since been warped and faulted? Wahlstrom (19^7) attacked this problem by studying the Tertiary rocks, especially the extrusive lava flows and pyroclastic materials. He studied the positions of the lava flows (mid-Tertiary) which occupy old valleys cut into the peneplain surface, and the pyroclastic material In the White River formation (Oligocene), Arikaree formation (Miocene), and the Ogallala formation (Pliocene) of the Great Plains. He noted that the lavas that filled the old valleys were also beveled by the erosional surface of the Flattop peneplain. If the volcanic activity was mid-Tertiary, then the erosion that produced the peneplain surfaces must have been later. 29 Wahlstrom believed the multiple-peneplain hypothesis to be unsatisfactory. He wrote that one extensive pre-Pleistocene old-age surface existed. This surface probably reached its maximum development in late Pliocene or early Pleistocene. He says, "The apparent steplike relationship between the higher and lower surfaces emphasized in the two-peneplain hypothesis is explained as resulting from the erosion of a differentially upwarped and/or faulted, single, originally continuous surface" (Wahlstrom, 19^7, p. 571)- Therefore the Flattop peneplain of earlier writers is regarded by Wahlstrom as the lateral extension and time equivalent of the Rocky Mountain peneplain. If the ideas of Wahlstrom are to be accepted, and they do appear reasonable, the erosional surfaces at different levels are due to faulting, differential uplift, and later differential erosion.

Glacial History Numerous names have been given to the stages and sub­ stages of mountain glaciation throughout the Southern . This has led to a long and cumbersome list. Despite all of these names, the terminology that was first proposed by Blackwelder (1915) for the glaciations in the Wind River Mountains is now becoming standard for the whole Rocky Mountain region. Blackwelder recognized three glaci­ ations, Buffalo, Bull Lake, and Pinedale. He considered the Vaggalo to bejre-Wisconsin, the Bull Lake to be early 30 Wisconsin, and the Pinedale to be late Wisconsin (Table 4). Richmond (1948) modified Blackwelder1s Pleistocene sequence in the Wind River Mountains. He divided the Buffalo into three stages and indicated that they probable represent the Nebraskan, Kansan, and Illinoian stages of continental glaciation of the Mississippi Valley region. Richmond (1957s p. 239) stated that the three pre-Wisconsin glacial stages are widely distributed throughout the Rocky Mountains. Pre-Wisconsin till has been recognized in the area of investigation by Ives (1953a & b) Madole (I960 and 1963)s and S. E. White (personal communication) (Table 4). This till has not yet been divided into the three stages as Richmond suggested. The pre-Wisconsin till will be referred to as Niwot Ridge till, following Madole, in this dissertation (Plate I). These deposits occur on interstream summit areas and are believed not to be related to the valley glacial deposits. This till is thought to be the result of an ice cap which was not confined to the present valleys, but spread as an over the higher parts of the Front Range, pos­ sibly before the inner deeper valleys were eroded. Neoglaciation is represented by the Temple Lake stade and the Gannett Peak stade, both of which are named from the Wind River Mountains. Moraines of the Temple Lake stade are older and occur approximately one mile downvalley from the cirque headwalls. Moraines of the Gannett Peak stade occur a few hundreds of feet beyond the existing glaciers of today. 31 TABLE 4. Correlation of stages and substages in the area of investigation with Rocky Mountain region.

1 "■ “ 1 Upper Silver Lake Rocky Mountain South St. Vrain Valley Region Valley Madole Ives (1953b) Richmond (1965) (I960) modified after Rlaclfwelder flQIS}

Modern Recent and Gannett Peak Moraines Modern Stade Glaciations Isabelle Temple Lake Substage Stade Neoglaciation Neoglaciation

Brainard Lake Upper Valley Late Stade Substage Stages Middle stade (2-3 Advances) Albion II Early stade Stage

Glaciation Pinedale 2nd episode

Upper Albion I Late Wisconsin Lefthand Creek Glaciation Stade 1st episode

Substage Stage

Bull Lake Bull Early stade i Sacagawea Ridge Glaciation o - Niwot Ridge Pretty Meadow rH Cedar Ridge

pre- Cm 3 Washakie Point

Wisconsin CQ Glaciation 32 The deposits of these two stades will be discussed in greater detail later. Benedict (1966, personal communication) has added an intermediate stade called Arikaree. This stade will be discussed later in more detail. Pinedale, Temple Lake, and Gannett Peak moraines are most common in the area. Moraines of Bull Lake age are ques­ tionable. Bull Lake moraines and most Pinedale moraines are best developed far downvalley from the area of study. DESCRIPTIONS OF MASS MOVEMENT FEATURES

Introduction It is not the intent of this investigation to describe every type of mass movement that has occurred In the area of study. The more distinctive and characteristic features were chosen. They are as follows: rock glaciers, possible rock glaciers, protalus lobes, proscree lobes, protalus ramparts, scree sheets, avalanche boulder tongues, complex talus cones, alpine mudflows, and rockfall talus. These features were described from field observations by the writer and then related to work done by other authors on similar features. Every individual feature in each valley studied will not be described; instead, those thought to be most representative were selected. It should be noted that many of the features mentioned above are related and dependent on each other; for example, talus cones are composed of mudflow, rockfall, and avalanche debris.

Alpine Processes of Erosion Following are a number of types of erosion and mass movement considered important in this area of Colorado. Most of these processes Individually appear to have only minor significance in the denudation of the area, but it is the

33 34 combination of these processes that makes them important. According to Sharpe (1938, P* 17), flow and slip are the two principal forms of mass movement. To these two, Rapp (i960, p. 74) adds "fall." 1) Flow— Flow is movement by continuous plastic defor­ mation. It Is represented by mudflows and solifluction. 2) Slip— Slip is movement without continuous deforma­ tion over a slip plane. This is the basic type of movement in . 3) Fall— Fall Is movement by free fall or by leaping or bounding down slope. It should be noted that neither the above principles nor the following processes include weathering. Weathering, whether it is chemical, mechanical, or both, supplies the rock debris that enables the processes of mass movement to take place.

Creep— According to Rapp (i960, p. 74), creep is the slow imperceptible flowing or sliding mass movement. Examples are rock creep, talus creep, soil creep, and solifluction (Sharpe, 1938, p. 20). a) Rock creep— Rock creep Is represented by the move­ ment of joint blocks of massive rocks. This occurs along the valley walls where blocks move along joint planes. b) Talus creep— Sharpe (1938, p. 30) defines talus creep as the downslope movement of a talus or scree, or any of the material of a talus or scree. This 35 slow downslope movement of debris appears to occur on most of the mass movement features to be dis­ cussed; however, it is thought to be of minor importance. c) Soil creep— Soil creep occurs on almost every soil covered area in this alpine region. Soils on the mass movement forms, valley sides, and ridge tops all show evidence of soil movement. d) Solifluction— Andersson (1906, p. 95) defines solifluction as "slow flowing from higher to lower ground of masses of waste saturated with water (this may come from snow melting or tain)." Features of solifluction, although not a topic of specific concern in this dissertation, do occur in the area. They are most common along flattopped ridges where meltwater and rainwater collect to saturate the underlying debris.

Rockfall— Rockfall means the more or less free falling of rock particles of any size from steep walls or cliffs. This type of mass movement is an important contribu­ tor of rock debris to mass movement features in the area. Free falling is the most rapid of all mass movement.

Rockslide— Sharpe (1938, p. 76) states that rockslide is "the downward and usually rapid movement of newly 36 detached segments of the bedrock sliding on bedding, joint, or fault surfaces or any other plane of separation." This type of mass movement is common along the valley walls and the couloir walls.

Alluvial processes a) Ralnwash and meltwater wash— Although rainwash and meltwater wash may seem to play a small role in the processes of alpine erosion, it is believed they are important. This water is thought to have trans­ ported fine rock particles downward into and away from many of the mass movement features. b) Sheetwash— Sheetwash is a thin sheet of water flow­ ing over the ground or rock surfaces, and carrying fine particles. This type of erosion is thought to take place high on the valley walls where it trans­ ports fine particles down the valley sides and into the couloirs. This is also known to take place on the faces resulting in fine particles being deposited at the cliff base. c) Mudflow— Mudflows are rapid forms of mass movement, generally consisting of a wet mixture of fine grained material, cobbles, and boulders. Mudflows will be discussed later in more detail. 37 Snow avalanching— Snow avalanches have been divided by S. E. White (personal communication) into: (a) clean dry snow aralanches, (2) clean wet snow avalanches, (3) dirty dry snow avalanches, and (4) dirty wet snow avalanches. These terms are self-explanatory and differ in their content of water and debris. Clean snow avalanches are characterized by an occasional boulder carried in clean snow. Dirty snow avalanches are characterized by the transport of all sizes of rock debris in snow.

Rock Glaciers Introduction Sharpe (1938, p. ^3) defines rock glaciers as "glacier-like tongues of angular rock waste usually heading in cirques or other steep-walled amphitheaters and in many cases grading into true glaciers." They are most common in regions that have been recently glaciated. According to Richmond (1962, p. 20), a rock glacier is "a tongue-like or lobate mass of rubble, locally with a core of till-like debris, that has surface features resembling some of those of glaciers." They are commonly longer than they are broad. Rock glaciers were first discussed by Spencer (1900) and Cross and Howe (1905) in their work in the San Juan Mountains of southern Colorado. Cross and Howe referred to rock glaciers as rock streams. Capps (1910, p. 359) was the first to use the term "rock glacier" in print. 38 Wahrhaftig and Cox (1959) in their study of rock gla­ ciers in the Alaska Range, Alaska, grouped them into three types on the basis of their shape, ratio of length to breadth, and topographic position. Lobate rock glaciers are as broad or broader than they are long. They are single or multiple lobes that originate at the base of talus cones. In this study these lobate forms will be referred to as "protalus lobes" after Richmond (1962, p. 20). The reason for this dis­ tinction will be discussed under protalus lobes. Tongue- shaped rock glaciers almost fill cirques. They are by definition longer than they are broad. It is evident that tongue-shaped rock glaciers also conform to the definitions proscribed by Sharpe and Richmond. The term "rock glacier," used in this Investigation, refers only to the tongue-shaped form. Spatulate rock glaciers develop when the front section of a tongue-shaped rock glacier is permitted to spread later­ ally. This type is not present within the area of investiga­ tion. A number of rock glaciers are present in the Colorado Front Range, but only one that may be termed "rock glacier" without controversy lies within the area of this report, the Arapaho rock glacier. Fair rock glacier on the west side of the Continental Divide (Plate I) and Taylor rock glacier In Rocky Mountain National Park are mentioned only in connection with rates of movement as determined by S. E. White. 39 The exact origin and nature of movement of rock glaciers is still somewhat in doubt. The writer's opinion of the origin and movement will be given, along with ideas of previous investigators who have worked on the Arapaho and other rock glaciers.

Arapaho Hock Glacier Location: Arapaho rock glacier lies at 40° 1' 12“ north latitude and 105° 30' west longitude. It occupies the southernmost cirque in the double cirqued Arapaho Valley. The rock glacier occupies the entire cirque floor, which, Incidentally, lies just below and east of the Continental Divide (Plate I). The front is at an altitude of approxi­ mately 11,720 feet whereas the head, located beneath the cirque headwall, is at approximately 12,160 feet. South Arapaho Peak, with an elevation of 13,397 feet, rises above the cirque headwall due west of the rock glacier. Relief in this cirque from rock glacier head to South Arapaho Peak is approximately 1,237 feet.

Description: Arapaho rock glacier is tongued-shaped, approx­ imately 825 feet wide, and 2,000 feet or more in length. The true thickness is rather difficult to determine because the cirque floor is nowhere exposed. An estimate would be 70 to 90 feet of thickness In the downvalley half. The average slope of the front of the rock glacier is approximately 46°; that of the sides is about 39°. According to Wahrhaftig 40 (1959* p. 387), the head is the place where a rock glacier merges with a glacier, or where it ends abruptly at a pit formerly occupied by a glacier. The head of Arapaho rock glacier ends in a shallow depression, but the bottom of this depression is occupied by a glacier buried by talus and rock­ fall debris being derived from the cirque headwall. The upper surface of the rock glacier slopes rather gently downvalley (16°). Diagnostic microrelief features exist on this surface, the most prominent of which are sets of nearly parallel transverse ridges and furrows. Wahrhaftig and Cox (1959, P- 392) describe such transverse ridges on Alaskan rock glaciers as being rounded and the furrows between as being V-shaped. This appears to be true of many Colorado rock glaciers, especially those observed in the San Juan Mountains, However, cross sections of the ridges and furrows of the Arapaho rock glacier are in most cases asymmetrical with the steep portion of the ridges facing outward toward the sides and front (Fig. 4, longitudinal profile). The height of the ridges, measured from the bottoms of the furrows to the tops of the ridges, ranges from 12 to 20 feet. The top surface of some ridges is tilted and slopes backward toward the head (Fig. 4, longitudinal profile). Longitudinal and transverse ridges are present, but the latter are much more common and conspicuous on this rock glacier. Longitudinal ridges parallel the sides for short distances and then curve toward the center to form transverse ridges. Longitudinal ridges are most common 41

(North Arapaho PRG [ Peak , 13502 r Gannett ^ Peak Moraine

V a l l e y

Ridges

Snow

South Arapaho Peak

Plan V iew

0 1300 1950

Pig. 4.— Plan view (left) of Arapaho rock glacier (green) at the head of Arapaho Valley, with transverse ridges, longitudinal ridges, meandering central furrow, and showing relationship to Arapaho ice glacier, possible rock glacier (PRG and red), cirque, and Gannett Peak moraines. X repre­ sents convergence of ridges and furrows. Longitudinal profile (right) of Arapaho rock glacier. X represents point of convergence of ridges and furrow. 42 on the upvalley half but even here they are rather weakly developed (Fig. 4, plan view). This is probably because the longitudinal portions of the ridges were destroyed or over­ ridden by later forward and lateral movement of the rock glacier. Another striking surface feature is a meandering incised furrow extending longitudinally down the center of the rock glacier. This furrow is not identifiable in the lower portion (Fig. 4, plan view). It is believed by the writer to be a collapse feature caused by meltwater which flows through the rock glacier and drains the glacier and snowbanks in the cirque to the west of the head of the rock glacier. The stream melted the ice as the glacier retreated and also removed the finer materials, both events allowing the coarser debris to collapse and form the furrow. This feature is referred to as a '.'meandering furrow" by Wahrhaftig and Cox (1959, p. 392). Two smaller less conspicuous surface features are pits and conical hills. The pits, usually only a few feet deep and irregular in outline, are probably collapse features caused by melting ice. The hills are rather difficult to explain because some are almost perfectly conical in shape, rise 10-12 feet in height, and have a basal diameter of 10-15 feet. Some have the appearance of having been pushed up from below. The writer has no other explanation as to the origin of these small hills or knolls except that they may be caused by 43 differential pressure exerted during the advance or read­ vances of the rock glacier. The Arapaho rock glacier consists of rock debris and ice. The rock component ranges in size from blocks as much as 20 feet in diameter to silt and -size particles. Mechanical analyses of the finer material collected from the front of the rock glacier indicate a content of 40 per cent sand and 5 per cent silt and clay for particles less than 4mm. The overall composition resembles till. Nearly all blocks are angular or subangular; none are faceted or striated. A very striking feature is the sorting of the rock debris into two layers, an upper layer mainly of coarse blocks and a lower thicker layer of sand and silt with minor coarse blocks. The front of the rock glacier and each ridge that completely traverses it (Pig. 4) appear to be divided into these two textural layers (Fig. 5). The exact mechanism by which this crude sorting takes place is not known; it may have been caused by a roller bearing effect which took place during forward movement. As the debris was pushed forward and in some cases slightly upward, finer material migrated downward between and under the larger boulders. The downward migration of fines may have been facilitated or caused completely by continued rainwash or meltwater carrying fine particles down­ ward. If all fines were removed from the rock glacier, the appearance of the bottom layer might be similar to the coarse upper layer. In summary, It is possible that the 44 layering effect is the result of removal of fines from the upper layer and redeposition In the lower layer. Ice appears to be a very Important component of the Arapaho rock glacier. Two types of Ice were found. Glacier ice, with a minimum thickness of 45 feet, was found beneath the upvalley one-third of the rock glacier (Fig. 7). This ice lies beneath 1 to 2 feet of rock debris and contains shear planes which dip upvalley at angles of 40 to 45 degrees (see photograph, Outcalt and Benedict, 1965). Organic material in the shear planes has been dated by the radiocarbon technique and shown to have an age of 1000 +90 years B.P. (A.D. 950) (Benedict, 1967, personal communication via S. E. White). Glacier Ice was not detected at the front, but blasting did reveal interstitial ice around rock particles in one of the ridges near the front. This ice probably resulted from water that was trapped and frozen. Capps (1910, p. 362), in describ­ ing rock glaciers in Alaska, states that interstitial Ice was found in every glacier studied. A situation that may be quite comparable to that of Arapaho rock glacier was described by Brown (192 5) when a mining tunnel was constructed through a rock glacier in the San Juan Mountains. The first few feet of the tunnel penetrated typical rock glacier debris. The next 300 feet consisted of rock debris cemented by ice. The last 100 feet of tunnel penetrated clean ice. The writer suggests that the same conditions are present beneath Arapaho rock glacier with interstitial ice in the front two-thirds and glacier ice in the upvalley one-third. Foster and Holmes (1965, p. 84) suggest that the ice content of a rock glacier in the Johnson River area, Alaska, was probably one-tenth to one-fourth of the volume of the rock glacier. An estimate at this stage may not yet be given for the Arapaho rock glacier but the estimate made by Foster and Holmes seems quite comparable to the rock glacier here.

Evidence of Motion: A number of features associated with the rock glacier indicate it has moved in the pafct and is still moving at present. The most conclusive evidence of past movement is the pattern of longitudinal and transverse ridges and furrows on the surface. In plan view, these features give an appearance of viscous fluid. The sorting of the rock debris into coarse and fine layers may indicate past movement to account for this separation, although this is doubtful. Numerous features indicate that movement is presently taking place. (1) The steep slope (averaging 40° and varying from 37° to 42°) of the front of the rock glacier and fronts of the longitudinal and transverse ridges (White, 1965, p. 9) Indicate that movement has been very recent in order to main­ tain this high angle at and above the expected so-called . Angles of the upper portions of the front are always greater, suggesting that the top portion of any lobe moves faster than the bottom. (2) The fronts of the rock glacier and the ridges are very unstable and can be walked on only with caution and difficulty. Large blocks may many times 46 be seen and heard rolling from the front of the rock glacier. Small mudflows are common along the front shortly after light rains (Fig. 6). With visible evidence of mass movement, it Is apparent that movement must be taking place to maintain the high angles. (3) Fronts of the rock glacier and the ridges appear as fresh surfaces because and other plants seldom grow there. This absence of vegetation is undoubtedly caused directly by the instability of these surfaces. (4) Some large blocks have a single lichen-free surface exposed or a lichen-covered surface lying face down. This indicates the boulder has been turned over recently. (5) Motion studies, whose results are to be discussed later, have yielded positive evidence that the rock glacier is moving. Lichen is the most common form of vegetation on the rock glacier. It is on most of the boulders except those on the fronts of the ridges, and on the front and sides of the rock glacier. Lichen is also absent in the longitudinal and transverse furrows, and the meandering furrow, but here it is due to long stay of snow each summer in the depressions. Following are a few plants that are present: Cirsium hookeranlum (thistle), Oxyrla digyna, Polenonium viscosum (Sky Pilot), and Senecia anplectaus (Ragwort) (Ronald Laughlin, personal communication). These plants are common wherever fine material is available for the development of root systems. They take root quickly and some even become established on the unstable fronts. Despite this, however, they are sparse on 47

Fig. 5.— View upvalley of Arapaho rock glacier, Arapaho Valley, Showing two textural layers (C=coarse, F=fine).

Fig. 6.— View of front of Arapaho rock glacier, showing small mudflows and debris that have flowed and slid down the front. 48 the fronts and have become best developed on ridge crests where small amounts of fine material are locally present.

Origin: Two problems are involved when attempting to estab­ lish the origin of rock glaciers. First, the origin of the debris is not well established. The debris could be from a moraine or moraines, from a or from a talus accumu­ lation. A combination of the above must also be considered. Secondly, what is the method by which movement has taken or is taking place? Is the movement due to modern interstitial ice, old buried glacial ice, gravity, or a combination of these three? Due to the nature of most rock glaciers, it Is nearly impossible to determine accurately and fully their internal composition. A number of theories have been presented concerning the origin of rock glaciers. A few of the more accepted theories will be stated briefly and certain Ideas from them will be combined with the writer's opinions in order to post­ ulate the possible origin of Arapaho rock glacier. It should be kept in mind that different theories may be correct for different rock glaciers or even different parts of the same rock glacier. Howe (1909, pp. 49-54) expressed the view that rock glaciers are the result of landslides that deposited rock debris on the surface of small glaciers and snowbanks during the waning stages of the last ice age. The wrinkled surface is the result of the outward flow of the slide debris. Capps 49 (1910, p. 364) advanced the theory that water from melting ice and snow sank into debris, derived mainly from the cirque headwall, that had accumulated on the surface and in front of dying glaciers. The water froze and gradually filled the interstices with ice. Melting and freezing caused incipient glacial movement. Chaix (1923, p. 32) maintained that move­ ment was due to interstitial mud and clay which lubricated the debris and allowed down-slope movement. Ivew (1940, p. 1274) referred to Fair rock glacier as a "runaway" terminal moraine and said that it represented the youthful stage of a rock glacier. He believed that movement was caused by thrust­ ing of interstitial ice. Kesseli (1941, pp. 218-225) referred to rock glaciers as being of glacial origin. He believed they are relict features. Low and short ridges that are subparal­ lel to the trend of the rock glacier were caused by overriding ice. The present configuration is due to creep or a remain­ ing core of ice. Richmond (1952, p. 1292) proposed that rock glaciers once contained ice cores and that the ridges and furrows are due to small glacial advances. Wahrhaftig and Cox (1959, p. 432) supported Capps by stating that active rock glaciers are masses of debris and interstitial ice and owe their motion to the flow of interstitial ice. Outcalt and Benedict (1965, pp. 850-855), after studying rock glaciers from vertical aerial photographs in the Colorado Front Range, stated that rock glaciers represent debris-covered tongues of true glaciers that formerly occupied the floors of cirques. 50 It is the opinion of the writer that none of the theories stated above are suitable in their entirety as an explanation for the origin of Arapaho rock glacier or other rock glaciers observed in the Colorado Front Range. However, numerous ideas from each seem applicable here. One important fact that has permitted the writer to be more positive in his conclusions Is the discovery on August 28, 1967, of a minimum of 40 feet glacier ice with distinct shear planes beneath the upvalley one-third of Arapaho rock glacier (Fig. 7)* To the writer's knowledge, this is the first discovery of glacier ice beneath a rock glacier. Numerous authors have mentioned the presence of interstitial Ice; Brown (1925* p. 465) mentions clear ice; other authors have speculated, that glacier Ice was present, but none had actually discovered unquestionable glacier ice. Plant material in the shear planes yielded a date of 1000 +90 years B.P. (Benedict, 1967* written communi­ cation via S. E. White). This age of the plant material, which dates the glacier Ice in the rock glacier, is between Temple Lake (3800-2000 years B.P.) and Gannett Peak (began 300-400 years B.P.) stades. To the 1000 +90 years B.P. age, Benedict has given the name "Arikaree Stade." Ages of the glacial features and their relationships to mass movement features will be discussed later in more detail. The knowledge that a glacier or relict glacier does exist beneath at least part of the rock glacier, leads this Investigator to believe that Arapaho rock glacier Is, for the most part, glacial in origin. It is believed that glacier 51 ice caused past movement, Is responsible for most of the present shape and surface features, and may still be an impor­ tant factor of present movement. It is thought that the glacier carried abundant debris on top and within the ice, and at the same time pushed and deposited debris at its front. Therefore, much of the debris is probably morainal. Glacier ice was found only beneath the upvalley one-third of the rock glacier, none has yet been discovered near the front. Attempts to dynamite a hole into the northern edge near the front yielded only interstitial ice. It appears that glacier ice may not be present in the front two-thirds of the rock glacier. This leads to several additional problems. If the underlying glacier ice is moving, then is this movement the cause of movement of the rock glacier, and why does the down- valley two-thirds of the rock glacier move if It does not contain glacier ice? Rock debris in the front lies at and above the expected angle of respose, suggesting that present movement must be responsible for the maintenance of this angle. Survey lines across the rock glacier reveal that movement is taking place over most of the rock glacier (Fig. 55). A tunnel through a rock glacier in the San Juan Moun­ tains revealed, at the time of tunneling, interstitial ice In the front three-fourths of the rock glacier and clear ice in the upvalley one-fourth (Brown, 1925). The same situation Is thought to exist In the Arapaho rock glacier with the down- valley portion consisting of interstitial ice and the upvalley 52 one-third being true glacier ice. If this is the case, the present movement of the rock glacier can be attributed to three factors; (1) The buried glacier still exerts some downvalley push. Movement of debris along shear planes will add some material to the back of the rock glacier. Any advance of the Ice will cause at least the upvalley portion to move. (2) Since the cirque floor probably has considerable slope (15° to 25°), each succeeding ice advance would deposit debris on top of older debris that was deposited by a previous advance. As a result, the rock glacier Is step-like as shown in the longitudinal profile of Figure 4. The resulting transverse ridges and furrows suggest glacial movement. Material added by rockfall and talus from the cirque headwall also add to the amount of accumulating rock debris. (3) In­ terstitial ice probably plays a very important part in the downvalley migration of the rock glacier. Interstitial Ice, aided by the effects of gravity on the accumulated rock debris, permits downvalley migration of the deposit as a unit very similar to the movement of an ice glacier. Interstitial Ice provides lubrication for the rock debris and may contain crude shear planes. In summary, present movement is due to a combination of effects of glacier ice, interstitial ice, slope, and gravity. From the data presented above, the writer believes the origin of the rock glacier is basically glacial. The buried glacier may have extended downvalley nearly to the front of 53 the present rock glacier. This extension could have been an advance in late Temple Lake or Arikaree times. The advance probably occurred at a time following a period of intensive accumulation of rock debris on top of and in front of a small cirque glacier. The upper part of the cirque may have been nearly filled with talus and rockfall debris. The advancing glacier may have pushed the debris in front of it much like a bulldozer. The possibility also exists that the glacier never extended to the downvalley position at which the lower two-thirds of the rock glacier is now located. The lower two-thirds of the rock glacier may have resulted from the buried glacier pushing debris downvalley. The buried glacier may not have extended beyond its present position but merely pushed and deposited debris at its front, which with the additional aid of gravity and interstitial ice, moved downvalley and away from the glacier to form the present rock glacier. The debris-ladened glacier may have retreated and advanced a number of times. Due to the slope of the cirque floor, each advance may have resulted in material being pushed on top of debris deposited by the preceding advance. The convergence of the ridges and furrows into a single plain or ridge at the side of the rock glacier supports this theory by showing that there has been an overriding of successive deposits. Figure 4 shows how the ridges and furrows converge. The overriding and pushing resulted in the formation of 54 ridges and furrows. The source of debris appears to be two­ fold: (1) till, probably contributed by glacial erosion, and (2) much rockfall and avalanche debris derived from the cirque headwall. A number of reasons exist why the rock glacier formed in Arapaho cirque: (1) The rugged mountains, with a northeast- facing cirque having a steep headwall and sides, present a favorable location for the formation and maintenance of glaciers. (2) Climatic conditions of the area appear to be favorable to glacial activity. The presence of the buried glacier and Arapaho glacier attests to this. (3) Freeze-thaw conditions are favorable to rockfall and avalanching. Joints in the cirque headwall are abundant and allow repeated freezing and thawing to loosen large amounts of material. Local relief of approximately 1,2 37 feet is a contributing factor to rapid mass movement of debris into the cirque.

Possible Rock Glaciers As stated, only one well-defined rock glacier is in the area of study. The writer, however, recognized three similar features that may be rock glaciers. They will be described under the heading of possible rock glaciers; they are probably rock glaciers that have not developed such well defined features as Arapaho rock glacier.

Arapaho Possible Rock Glacier: This feature is on the north side of Arapaho cirque. Movement is from the north cirque of 55 the Arapaho double cirque (shown In red In Pig. 4, plan view). At first appearance, this feature appears to be a series of slump blocks from the Gannett Peak moraine in front of the Arapaho glacier. However, three factors appear to disprove this possibility. (1) A study of serial photographs suggests that the debris moved in an orderly manner from the north portion of the cirque. (2) Poorly developed ridges display the same type of sorting into a fine and coarse component as do those on the Arapaho rock glacier. This type of sorting Is not present on the Gannett Peak moraine. (3) Although the writer knows very little concerning the techniques of lichenometric studies, the lichens appear well-developed on this feature compared to little if any development of lichen on the Gannett Peak moraine. The lichen cover appears to be similar to that on the Arapaho rock glacier. The suggestions made above, plus the fact that this possible rock glacier and the Arapaho rock glacier nearly coalesce at their fronts, suggests that they are approximately the same age. Sufficient amounts of ice and debris may not have been available for the formation of a well defined rock glacier in this part of the cirque, because its position on the north side permitted it to be exposed more often to direct sunlight.

Henderson Possible Rock Glacier: This possible rock glacier is on the north side of Henderson cirque in Henderson Valley (Plate I). It Is mapped as a possible rock glacier but It Is 56

Pig. 7.— Buried glacier ice within Arapaho rock glacier, Arapaho Valley.

Pig. 8.— Arikaree possible rock glacier (PRG), Arikaree glacier (AG), and Temple Lake Moraines (TM) at the head of Green Lakes Valley. View is to the south. 57 very poorly defined. Ridges and furrows are poorly devel­ oped. The deposit appears to have been an accumulation of rockfall debris and scree that migrated into the cirque and on top of till thought to be late Bull Lake. Interstitial ice is probably the contributing factor to the ability of the debris to move. A definite difference in weathering exists between the till beyond and the debris of the possible rock glacier. A striking difference associated with this possible rock glacier is its position in the cirque. Unlike the Arapaho rock glacier and possible rock glacier, this feature has moved from north to south across the cirque instead of downvalley to the east. Another difference is that the ridges and furrows are not well developed. Two factors are probably responsible for the poor development of this possible rock glacier. (1) A steep high cirque headwall is not available from which large amounts of debris could be supplied. (2) The slope of the cirque floor is very gentle (not more than 12°) and does not encourage movement downvalley.

Arikaree Possible Rock Glacier: Arikaree possible rock glacier Is in Arikaree cirque on the north side of Arikaree Peak at the head of Green Lakes Valley (Plate I and Fig. 8). This feature resembles the Henderson possible rock glacier but is larger and much better defined. Ridges and furrows 58 are well developed although their relief is only about 5 to 6 feet. This possible rock glacier resembles the rock glaciers of the San Juan Mountains in that the crests of the ridges are rounded and the furrows are V-shaped. This is in direct contrast to those on the Arapaho rock glacier. An­ other difference is in the size of debris. Unlike on the other rock glaciers, the diameters of boulders and blocks usually do not exceed 3 to 4 feet. The possible rock glacier in Arikaree cirque resembles the Henderson possible rock glacier in that its movement has been across the east-west oriented cirque. Movement has been to the north away from the base of Arikaree Peak, into the cirque and out on top of probable morainal material. Absence of a steep cirque headwall may have been an important factor in determining the rate and amount of rock debris supplied. Despite the absence of a steep headwall, a large amount of debris is available from scree and , but it may not have been supplied in large enough quantity to make a distinct rock glacier. 59 Protalus Lobes Introduction Richmond (1962, p. 20) defines a protalus lobe as "a tonguelike or lobate mass of rubble or debris that is a product of creep or solifluction of the toe of a talus." Apparently for this very same feature, Wahrhaftig and Cox (1959, p. 389) use the term lobate rock glacier. They define it as consisting of single or multiple lobes extending out from the bases of talus cones or talus aprons. Such lobes most commonly are as broad as or broader than they are long. Outcalt and Benedict (1965, p. 856), describing similar features here and in other parts of the Colorado Front Range, use the term valley-wall rock glaciers. They refer to this feature as the accumulation of debris occurring beneath steep avalanche couloirs that supply large quantities of snow and debris to the valley floor. Richmond's term protalus lobe will be used instead of rock glacier because the word glacier is believed to be somewhat misleading. It Is believed that glacier ice is not present and has in no way influenced the formation and movement of these features. Instead, inter­ stitial ice is thought to be the important constituent within the pore spaces of the deposits. One stipulation concerning the use of protalus lobe that should be made is that the lobe must be in direct association with talus or similar debris such as that derived mainly by avalanche, mudflow, or rockfall via chutes and couloirs along the valley wall. Similar lobes 60 formed on scree slopes are here referred to as proscree lobes. The number of protalus lobes within the area is diffi­ cult to determine because some lobes are so closely spaced they coalesce along a valley wall. In a few places the lobes are superimposed. Three large complexes of coalescing protalus lobes (Plate I) are on the north side of Arapaho Valley north of Goose Lake, on the south side of Isabelle Valley southeast of , and on the south side of Blue Lake Valley south and southeast of Blue Lake. Because of the number of protalus lobes, each one will not be dis­ cussed separately, but rather a general description pertaining to all lobes is offered and a limited number of selected examples described. Every characteristic listed will not per­ tain to each protalus lobe.

Location Protalus lobes are common In every main valley and tributary valley except Henderson Valley. Forty-one protalus lobes were identified (Plate I); of these, 8 are bilobate (Fig. 50); 3 are multilobafre (consisting of more than 2 lobes, Figs. 31 and 40); and 30 are single lobes (Fig. 11). The 3 multilobate protalus lobe complexes contain 16 lobes. Thus the 41 protalus lobes contain at least 62 individual lobes. Twenty-two of the 41 protalus lobes are on the south sides of the valleys, 14 are on the north sides, and 5 are on 61 slopes that face east. Of the 11 bilobate and multilobate protalus lobes, 4 are on the north sides of the valleys whereas 7 are on the south sides. Fifteen of the 30 single protalus lobes are on the south sides of the valleys, 10 are on the north sides, and 5 face east. Most of the protalus lobes occur on the south side of the valleys; likewise by far the greater volume of debris is also represented here. In addition, most of those on the south sides are much larger than the others.

Description Because the protalus lobes are single, bilobate, or multilobate, their shapes are variable. Most Individual lobes are symmetrically lobate. Lengths vary from approximately 75 to 1,000 feet and widths from 200 to 2,000 feet. Steepnesses of the fronts are similar to those of rock glaciers. Fronts of protalus lobes that appear active have angles ranging from 42° to 53°. Angles of the top surface range from a 22° slope away from the valley side to 0°, and in some cases part of top surface slopes toward the valley side. Thicknesses vary from 15 to 90 feet (Fig. 9). Depressions between recent talus and the protalus lobes are common (Fig. 15). Transverse ridges and furrows are not common and, wherever present, are usually discontinuous and poorly developed. Composition of protalus lobes Is similar to that of rock glaciers such as Arapaho rock glacier. The rock debris is separated Into a coarse bouldery surface layer and a finer Fig. 9.— Side view of protalus lobe at north base of Kiowa Peak, Green Lakes Valley. This is the location of motion study 6. Lobe is approximately 65 feet thick.

%

Fig. 10.— Movement of soil over edge of protalus lobe complex, Isabelle Valley. Fig. XI.— Protalus lobe (PL) and avalanche boulder tongue (ABT), south side of Green Lakes Valley. Lobe is in Green Lake # 2.

Fig. 12.— Mudflow on and around poorly developed protalus lobe, south side of Green Lakes Valley between lakes § ^ and # 5- Line shows position of motion study 9- 64 underlying layer. Mechanical analyses of the finer material collected from the front of the bilobate protalus lobe in Pawnee Valley indicate a content of 73 per cent sand and .35 per cent silt and clay for particles less than 4 mm. Fresh rock debris, supplied by mudflows, rockfalls, and avalanches, is common on top of and on the back portion of many protalus lobes. Boulders 15 feet in diameter are common. The ice component is still in question, but it is probably interstitial and not relict glacier ice. Evidence of inter­ stitial ice is as follows: (1) Small ponds of water occurred in depressions on three protalus lobes. These ponds, ex­ plained later in more detail, appear and disappear periodi­ cally. The high porosity of the protalus lobes should not support the existence of these ponds. Water should rain quickly unless interstitial ice and frozen debris prevent downward movement. In a depression on the protalus lobe com­ plex south of Blue Lake, water was present through the summer (Fig. 16). (2) Springs emerge from beneath the fronts of the protalus lobe complex south of Blue Lake Valley and the bilobate protalus lobe south of Green Lake No. 5 in Green Lakes Valley. Temperature of the water is 32° F. even in late summer. Ground water from summer rains or melt water from snowbanks in the couloirs or on the protalus lobes should not yield water with this low a temperature. The temperature should be higher if it percolated through the protalus lobe. Based on these reasons, the low temperature may be due to 65 melting of interstitial ice, melt water running through pores in the ice, or both. (3) Water emerges at a point approxi­ mately two-thirds distance up the front slopes of the protalus lobe complex in Isabelle Valley (Fig. 40) and the bilobate protalus lobe in Pawnee Valley (Fig. 47). This sug­ gests that interstitial ice is present up to that level in each lobe. Melt water may flow over the ice surface and emerge at that level on the lobe fronts. (4) On several of the lobes, spaces between boulders are large enough for one to see to depths of 10 to 12 feet. At the bottoms of many of these spaces, ice can be seen around boulders. This may be interstitial ice or ice resulting from snow that has blown in, melted, and refrozen. Considerable visual evidence shows that many of the protalus lobes are moving. This is supported by actual measurements, to be discussed later. Steep fronts, ranging from 42° to 53°, indicates that movement must be taking place in order to maintain these high angles. Many fronts have fresh-appearing surfaces with no vegetation in the fine material, all of which indicates instability. Instability is further indicated by mudflows and rolling debris on the lobe fronts (Fig. 40). Soil on a number of the lobes appears as if it is being pushed over the upper edge of the lobe front (Fig. 10), but actually debris at the front is dropping away from the soil on top. On two lobes, pits dug in finer surface material reveal buried soils, which indicate that overriding 66 slumping, or solifluction has taken place. Small mudflows also may have moved onto the protalus lobe surface, burying the soil.

Origin The origin of protalus lobes is still in question mainly due to the difficulty of determining their internal character. Wahrhaftig and Cox (1959* P* ^33) attribute the formation and movement to interstitial Ice that formed in the toes of talus accumulations. They believe the origins of protalus lobes and rock glaciers to be the same. Richmond (1962, p. 20) states that protalus lobes are the product of creep or solifluction of the toe of a talus. Outcalt and Benedict (1965, p. 856) believe that primary interstitial ice is the cause of formation. They define the primary ice as resulting from metamorphism of snow that was buried by rock- fall debris or supplied, together with boulders and finer material, by avalanching. Each theory postulates the presence of interstitial ice and the present writer agrees with the others as to its importance. Four factors, determined by present-day features, may be of major importance in the formation of protalus lobes. (1) Protalus lobes are located at the base of high, steep cliffs. Cliffs of this nature provide a large area from which rock debris may be derived and also provide the relief that supports rapid downslope movement of debris. (2) Maximum development takes place where joints are more intensely 67 concentrated. Joints serve two purposes: First; they provide the necessary space into which water can penetrate and then freeze and thaw to force the rock apart. This section prob­ ably provides the bulk of rock debris. Second; joints make possible the localization of couloirs down which the rock debris moves. (3) A high altitude seems to be important be­ cause it allows intense freeze-thaw action that provides much of the rock debris, and because it has a climate supporting the accumulation and maintenance of interstitial ice. (4) A large couloir or a sufficient number of smaller combined couloirs are necessary for localization of debris at the cliff base. Interstitial ice appears to be an important factor in the origin of protalus lobes. It is the only reasonable explanation why the talus toe moves out over the valley floor. Evidence In support of interstitial ice has been stated but the manner of its formation is still in doubt. This writer supports the theory of Outcalt and Benedict that much of the ice is probably primary in the sense that it is metamorphosed snow. The origin of this ice may be two-fold. Snowbanks may be burled by debris accumulating from avalanches, mudflows, or rockfalls. Also, the avalanches may transport and bury snow. In either case, buried snow is protected from evapor­ ation and summer heat by the overlying debris. Metamorphism of the snow changes it to interstitial Ice. Evidence for this theory is supported by the following sequence of events. In July of 1965 a mudflow, originating high on a cliff in Green Lakes Valley, moved down the valley wall both accumulating and depositing debris during its descent. Its course took it through rockfall debris, talus, and finally onto a snowbank and around the edge of a small protalus lobe (Fig. 12). The debris was composed of clay, silt, sand, and boulders with a thickness on the snow ranging from 3 feet to less them 1 foot. A mechanical analysis of the finer material shows a content 48 per cent sand and 7.5 per cent silt and clay for particles less than 4 mm. By September 1, 1965, the snow beneath the debris had become compact (Fig. 13), and by the summer of 1966, it had become ice (Fig. 14). Thus a small debris cover is sufficient to preserve snow and to permit it to be meta­ morphosed to ice. In summary, It appears that avalanches, mudflows, and rockfalls not only transport debris but also serve an important role In the accumulation and maintenance of Ice. The importance of Interstitial ice seems to be borne out in three protalus lobes that are thought to be stagnant. Two of these lobes occur below timber line; a multilobate com­ plex occurs north of Goose Lake in Arapaho Valley and a bilobate protalus lobe occurs north of Long Lake in Isabelle Valley (Plate I). Both lobes are on south-facing slopes and are covered by trees whose ring dates provide a minimum age of 550 years. If the trees are 550 years old, the protalus lobes must be older. The writer believes that they are stable 69

Pig. 13.— Mudflow debris resting on snowbank, Green Lakes Valley, summer 1965.

Pig. 1*1.— Mudflow debris resting on ice, Green Lakes Valley, summer 1966. Same location as Fig. 13, but snow has been metamorphosed to ice. 70 because their altitude, which is approximately 10,600 to 10,800 feet, is not high enough to maintain interstitial ice. Another example is the north-facing protalus lobe at the south edge of Green Lake No. 2 in Green Lakes Valley (Plate I and Fig. 11). Motion studies on this lobe reveal that it is stable. The lobe did not originally move into the lake; in­ stead, the lake level, due to the construction of a dam, was raised so that the lower portion of the protalus lobe is now below water (Fig. 11). It is quite probable that the water does not support the formation and maintenance of interstitial ice; therefore, with the absence of interstitial ice, the protalus lobe became stagnant. It is suspected that the rise of the water around the protalus lobe caused interstitial ice to melt. A large depression and few smaller ones at the back section of the protalus lobe near the cliff base may repre­ sent collapse due to melting of interstitial ice. It Is believed that interstitial ice Is the main fac­ tor accounting for the ability of protalus lobes to move, but this does not explain fully what the force is that causes the movement. In the case of glaciers, debris moves through shear planes and is deposited at the front and on top of the ice. The actual force Is the pressure due to accumulation of snow, later changed to firn and then to ice, at higher ele­ vations on the glacier. This force is then transferred down the glacier. The writer believes that a similar force is necessary to account for the movement of protalus lobes onto the valley floors. This force is thought to be exerted by the weight of debris in the lower portion of the couloirs and causing a resulting force downward toward the valley floor (Fig. 15). Large quantities of debris are common at the base of the talus and at the back portion of the protalus lobe. The force is eventually transferred out onto the valley floor. The debris is transported onto the rear of the lobes mainly by mudflows, but some is added by avalanches and rockfalls. The ability of the debris to move and the shape of the lobe are reflections of interstitial ice flow. Thus the formation and movement of protalus lobes are due to interstitial ice flow and the force of gravity on the talus debris.

debris accumulation depression-^.

valley floor

Fig. 15.— Longitudinal cross section showing theoretical forces thought to be necessary in the formation of protalus lobes.

Examples of Protalus Lobes A few selected examples are discussed to illustrate that not all protalus lobes display exactly the same features. Protalus lobes in the four valleys studied, Blue Lake, Isa­ belle, Green Lakes, and Arapaho, show distinct differences. 72 Blue Lake Valley: Protalus lobes in this valley are distinc­ tive in three ways. (1) Lobes are spaced so closely that they form an almost continuous strip of debris extending for more than a mile along the south valley wall (Fig. 16). No other valley contains a continuous assemblage of this nature. It represents a large volume of debris. (2) Most of the lobes have depressions in the back part of the lobe that partially separate them from talus descending from the valley wall, a feature that is not common to all protalus lobes. (3) Two lobes contain water-filled depressions (Fig. 16). The protalus lobe marked X in Figure 16 contains a depression in its back portion that was observed filled with water from July 19 to July 28, 1965. The pond was discovered on July 19 and the water level was marked. On July 20, the level was 17*5 inches lower; July 23, after three days of heavy afternoon showers, the level was up 35*75 inches from the original mark; July 26, the water level was only 14.75 inches above the marked level; July 27, the level was 27.5 Inches below the first mark; and on July 28, no water remained. As has already been discussed, interstitial ice may regulate the flow of water through the lobe, and movement within the lobe to allow passage of water at times and not at other times. The large multilobate complex, consisting of three large coalescing lobes, In the upper part of Blue Lake Valley on the southwest corner of the cirque also contains a depres­ sion. This depression, marked Z in Figure 16, was filled with Fig. 16.— Protalus lobes south side of Blue Lake Valley. A is location of motion study 2. X and Z show positions of water-filled depressions. B is Blue Lake. S is Shallow Lake. u> 74 water during the summers of 1965 and 1966. The level was not marked but it appeared to fluctuate only slightly during the summers. A spring, with a water temperature of 32° P. emerges approximately 20 feet beyond the front of the lobe. Un­ doubtedly the water comes from the protalus lobe and its low temperature may indicate the presence of interstitial ice.

Isabelle Valley: A multilobate complex of three coalescing lobes, shown in Figure 40, in Isabelle Valley is distinctive in a number of ways. (1) It is the largest complex in the area of study. Its volume and area may exceed that of any other protalus lobe or lobate complex studied. (2) Depres­ sions do not exists between the talus and the lobe; instead the relationship is gradational. The only notable depressions are between lobes due to lack of talus deposition. (3) The edge of the valley floor onto which this complex is built is much steeper than in other valleys. This is probably the cause for the steeper slope of the top of the protalus lobe complex. A maximum of 22° was measured for certain portions of the top. The steeper valley floor may also account for the lack of depressions between the area of modern talus accumu­ lation and the lobe surface. Depressions are most common on lobes that extend far out onto nearly horizontal valley floors. (4) Ridges and furrows are better developed on this complex. This may be due to a steeper valley floor, which allowed the lobes to acquire the characteristics of flow. (5) Water emerges from the middle lobe (Fig. 40) at a point approximately 35 feet up the front. This may indicate the presence of interstitial ice holding the water high inside the lobe.

Green Lakes Valley: Simplicity is the distinguishing charac­ teristic of protalus lobes in this valley. In comparison with those in other valleys, they are relatively small. No multilobate complexes occur and only one bilobate lobe is present. They are in most cases simple, single, symmetrical lobes that project only short distances onto the valley floor (Figs. 9 and 11). The protalus lobe at the base of Kiowa Peak is the best developed bilobate lobe in the area of investigation.

Arapaho Valley: The protalus lobe complex on the north valley wall north of Goose Lake displays a number of features that are not characteristic of lobes in other valleys. (1) This complex appears to be inactive. It is sparsely covered by trees, some of which have tree-ring dates of 550 years. The talus north and behind the complex is partly vegetated by grasses, shrubs, and small trees (Fig. 17). Presence of this vegetation indicates an essentially stable condition unlike that of the other protalus lobes described. (2) This is an extremely complicated protalus lobe complex. A minimum of ten lobes, whose positions are difficult to establish with respect to each other, compose the complex. As nearly as can be deter- Fig. 17.— Multilobate protalus lobe complex, north of Goose Lake, Arapaho Valley. Extent of lobe outlined in black. View is upvalley to the west.

Valle

R —*R idge t«j*Depre**ion

Fig. 18.— Sketch of lobes on protalus lobe complex shown in Fig. 17 above. 77 mined, the positions are shown in Figure 18. (3) A number of lobes are superimposed onto older lobes, a feature that occurs only on this complex lobe. For this reason it appears that numerous periods of movement took place. Material is being added to the top of this complex by avalanches and mudflows. Numerous trees have been broken by avalanche debris. Some smaller trees have been partially buried by mudflows.

Proscree Lobes Introduction Proscree lobe, a term proposed here by the writer, is similar to a protalus lobe in shape, but differs somewhat in origin and position on valley walls and slopes. Proscree lobes are smaller and form on scree slopes where rock debris is present as rubble sheets instead of being concentrated into talus. The lobes are single with a lobate or semi- lobate plan view. Most lobes contain depressions in their top central portions between the outer lobe edge and the scree slope behind. Accumulation of the debris into lobes is not attributed to movement of material through couloirs. Such a feature is distinct and sufficiently different from the other forms of mass movement reported on here to warrant this separate analysis.

t 78

Location Proscree lobes are developed on scree slopes. Plate I delineates the position of major scree slopes in the area, many of the steeper portions of which contain proscree lobes. Not all proscree lobes were mapped because of the large num­ ber of small lobes and because of their varying degrees of development. Only a few are mapped (Plate I). Locations of the more prominent lobes are as follows: (1) South-facing proscree lobes have developed on the northern scree slope in Henderson Valley. Two fairly distinctive lobes occur on the slope north of and above the debris accumulation mapped as possible rock glacier. (2) The north-facing talus extending from the col between Arikaree and Kiowa Peaks to the floor of Green Lakes Valley contains a number of proscree lobes in varying degrees of development. (3) Numerous lobes, most of which are small, occur on the scree slopes on the south side of Kiowa Peak and north side of Mount Albion. Both slopes descend to the remnant of an old erosion surface separating the two peaks. (4) Large portions of the north and south sides of Niwot Ridge consist of scree slopes. The north slope, which extends into Isabelle Valley, and the south slope, which descends into Green Lakes Valley, contain proscree lobes. (5) Sides of the ridge between Isabelle and Blue Lake Valleys contain lobes most of which are poorly developed. (6 ) The best development of proscree lobes occurs 79 on the scree slope, north side of Blue Lake Valley, north of Mitchell Lake. Here the several lobes, in comparison, are large and well developed (Fig. 19).

Description Proscree lobes occur on scree slopes where couloirs are absent. These lobes vary in size and degree of develop­ ment. Some are so small and poorly developed that their detection is difficult; others are large and developed to the extent that they closely resemble protalus lobes. Ridges and furrows do not exist. Fronts of most smaller lobes have angles of 28° to 35° whereas larger lobes, such as those shown in Figure 19, have angles of 37° to 41°. Better devel­ oped and larger lobes are on the lower one-third of scree slopes whereas smaller lobes can occur at almost any position. Rock debris and possibly interstitial ice appear to constitute the proscree lobes. Evidence of interstitial ice is lacking, but it does appear that such ice may have been important in the formation of proscree lobes because movement of debris into a lobate form is difficult to explain without interstitial ice as a means for movement. Sorting of the rock debris occurs only in two or three of the larger lobes whose upper surfaces consist of large boulders and whose lower portions contain boulders and finer material. The sort­ ing is crude. Boulders in proscree lobes are much smaller than those in protalus lobes. Diameters of 5 to 6 feet are maximum, but diameters of 2 to 3 feet are most common. 80 Origin The origin of proscree lobes is still in doubt. They are similar to protalus lobes in shape, but differ from them mainly in size and position on the valley walls or along the valley slopes. Similar to the proposed origin for protalus lobes, interstitial ice is believed to be an important factor in the formation of proscree lobes. It is believed that interstitial ice was concentrated, due to as yet undetermined or unknown factors, on certain portions of and at certain elevations on scree slopes. Formation and maintenance of this ice occurred for the period of time necessary for the forma­ tion of proscree lobes. Weight of rock debris on steep scree slopes plus the possible "lubricating11 effect of interstitial ice facilitated the downslope movement and the accumulation of debris into proscree lobes. The fact that couloirs are absent and cannot serve to concentrate rock debris may account for the small size of these features. There does not appear to be any relationship between occurrence and direction of exposure on a particular scree slope. The origin of proscree lobes may be similar to that proposed by Tyrell (1910, pp. 552-553) for rock glaciers. He suggested that rock glaciers "are kept supplied with water flowing from springs In the sides of hills; that this water becomes frozen Into a mass of Ice during the severe cold weather of winter; and that the Ice, with Its contained frag­ ments of rock, melt under the Influence of the warm weather 81 in spring." The present writer suggests that melt water may have been concentrated by means of joints causing it to emerge at positions corresponding closely to those of the proscree lobes. This melt water was frozen to form interstitial ice in the scree. Accumulations of the ice may be attributed to a period of cooling in late Pleistocene time. Interstitial ice was probably not annual but occurred during aperiod of time necessary for the formation of proscree lobes. In most cases, interstitial ice Is thought to be absent today.

Pig. 19.— Proscree lobes on scree slope north of Mitchell Lake, Blue Lake Valley. View east. 82 Protalus Ramparts

Introduction In two valleys, ridges composed only of angular rock fragments lie parallel to the steep valley walls. These ridges have been given different names, such as winter talus ridges (Lahee, 1931, p. 337), nlvation ridges (Behre, 1933, p. 630), and protalus ramparts (Bryan, 1934, p. 656). The term ascribed by Bryan will be used here.

Location Protalus ramparts have formed in Arapaho and Audubon valleys. The rampart in Arapaho Valley is small and is superimposed on a Temple Lake moraine. It is approximately 1,000 feet east of Arapaho rock glacier and on the south valley wall (Plate I). The protalus rampart in Audubon Valley Is large, distinctive, and parallels the north wall of the valley for nearly 2,500 feet. It is more pronounced in Its upvalley portion and, like the rampart in Arapaho Valley, it rests on a moraine.

Description Protalus ramparts are described as narrow elongate ridges that parallel steep valley walls (Bryan, 1934). A depression separates them from the cliff wall. They are composed of coarse angular rock debris almost completely of boulder size. A few of the boulders are as much as 10 to 15 feet In diameter but the majority are of 2 to 5 feet. Fine 83 material is conspicuously absent. The protalus rampart in Audubon Valley has a steep front (side facing the valley wall). The front slopes approximately 37° whereas the back slopes approximately 43°. The rampart ranges in height from a few feet to 23 feet. In some places the ridge is approx­ imately 100 to 125 feet from the cliff base.

Origin Protalus ramparts owe their formation to the existence of snowbanks that accumulate at the base of steep valley walls during winter months. The snowbanks may be annual or they may melt only during extremely warm summers. In either case, the snow serves as a surface of transportation over which debris moves from the valley wall to the front edge of the snowbank. The part played by the snowbank in the formation of the ram­ part ridge is such that it forms a barrier to deposition of talus from the cliffs above. Its location at the base of the cliffs does not allow falling rock debris to accumulate there; Instead, it causes material to roll or slide across the snow­ bank sind accumulate as a ridge on the valley floor. Scattered fresh boulders are present on top of the rampart in Audubon Valley. Since the distance between the rampart and the valley wall is approximately 100 feet, the most reasonable assumption is that the debris was transported across snowbanks that filled the depression between the ridge and valley wall during the winter and early summer months. Some avalanches may have served as the main means of transport. 84 Scree Sheets Introduction Scree is defined as rock waste at the base of a cliff or a sheet of coarse debris mantling a mountain slope. Talus is an accumulation of material at the base of a cliff; it includes loose material lying on slopes without cliffs. In this dissertation, the term scree will be used In reference to sheets of debris lying on slopes which have little or no cliff above to serve as source area. It includes rubble covered ridges where debris originally may have been partly till but has since been reworked by severe frost action. Richmond (1962, p. 19) refers to deposits of this type as "frost rubble sheets."

Location Major scree deposits are indicated on Plate I. Much of the material mapped as Niwot Ridge till, due to its poorly defined boundaries and questionable origin (Madole, i960 and 1963), also may be considered scree. Scree in this area is restricted to altitudes above timberline and Is closely associated with the old erosion surfaces that occur at the higher altitudes (Fig. 60). Scree sheets cover the upland remnants of these old erosion surfaces and in many cases descend almost to the valley floors. 85 Description Scree deposits are sheet-like accumulations of angular to subrounded rubble. Most of the debris is angular, the few subrounded boulders are thought to have been derived from till now incorporated into rubble sheets. Thicknesses of scree are difficult to determine, but they probably vary from a few inches to many feet. Most boulders do not exceed 2 to 3 feet in diameter. Scree sheets on the valley sides consist of coarse boulders whereas those on gentler slopes near ridge or divide tops contain fine material and in several places, such as on the old erosion surfaces, a good soil has developed. It is in the saddles and on the higher gentler slopes that solifluction and patterned ground are common. Nonsorted lobes (solifluction lobes), sorted polygons, sorted stripes, non­ sorted nets (earth-hummocks), and nonsorted circles (frost boils) have all formed on the scree. Slope angles of scree sheets vary from as much as 43° on the valley sides to only a few degrees near the ridge tops and saddles . Boulders on steeper slopes are unstable and appear to be near the angle of repose for their size. It is on these steeper slopes that proscree lobes, described in the previous section, have developed.

Origin Scree sheets are mainly the result of frost action. Freeze-thaw action and downslope movement mainly on parent material, but partly on pre-Wisconsin till, has resulted in 86 the present scree accumulations. The origin of the scree sheet on Niwot Ridge is three-fold: (1) Part of the deposit has developed entirely from angular debris derived directly from parent material beneath the scree or from a short dis­ tance upslope. (2) Part of the sheet is the result of frost action wholly within the Niwot Ridge till. Subrounded boulders are more common here. (3) Portions of the sheet appear to be a combination of both parent material and till. Within the area, scree sheets are most commonly developed on parent bedrock material. The association with till is com­ mon; Richmond (1962, pp. 80-81) Indicates that scree sheets may develop from till or solifluction mantle. Rapp and Rudberg (I960, p. 147), using the term "block-field zone" state, "if foreign erratic boulders occur to a great extent, it is possible that the block-field consists of glacial drift from which finer material has been removed or the boul­ ders accumulated on the surface by frost-heaving." As pre­ viously stated, many scree sheets are closely associated with the old erosion surfaces. It is believed that these surfaces were glaciated during pre-Wisconsin time by ice cap glaciation and a till sheet was deposited (Madole, i960). It is believed that post-Wisconsin glaciation cut the present valleys into this surface. Following pre-Wisconsin glaciation, different levels of the old upland surfaces have been exposed to inten­ sive frost action resulting in the development of scree sheets, in some Instances possibly above the later Wisoonsin valley glaciers. Complex Talus Cones Introduction Complex talus cones are cone-shaped deposits of rock debris whose shape has been controlled by movement of debris through a couloir or series of couloirs on the valley walls and whose origin is attributed to the combined accumulation of debris derived by rockfall, avalanche, and mudflow. These processes of deposition are important in the formation of com plex talus cones, but they are also related to rockfall talus avalanche boulder tongues and mudflow debris.

Location Complex talus cones are numerous in the area. Few places exist along valley walls that do not display complex talus cones or rockfall talus. They are of various sizes, but most are large and extend from near the ridge tops to the valley floors. Only a few are specifically mentioned; the more prominent are shown on Plate I.

Description Complex talus cones are associated with couloirs on valley walls. Coalescing complex talus cones and rockfall talus are common where couloirs are closely spaced (Fig. 20). Single couloirs do exist but most are a series of con­ verging couloirs that collect rock debris from rather large areas. Complex talus cones may serve as feeder talus to protalus lobes (Fig. 40) or form single cones along valley 88 walls (Fig. 44). Slope angles may be low on portions of the toe near the valley floor, but angles of 40° are common on higher parts of cones that project upward into the couloirs. Coarse debris is common high on the cones, especially in that portion confined to couloirs, and on the lower part of cones where fall-sorting (gravity-carried debris at distal part of cone) occurs. Fine material is most typical in the central half of the cones. Rockfall talus cones, showing coarse debris at the bottoms and fine material at the apex, occur but most of them are smaller. In Figure 20, cone D is a rockfall talus cone. Meltwater and rockfall are probably the main factors of deposition. Cones A, B, C, and E have coarse debris at both the tops and bottoms; rockfalls, avalanches, meltwater from snow and ice, and mudflows probably account for their deposition. Complex talus cones are charac­ terized by instability. Higher portions are usually less stable. Rock debris rolls, slides, rotates, and is removed, deposited, and displaced by mudflows, meltwater, rockfalls, and avalanches. Boulders may be 15 to 18 feet in diameter, but they are not abundant. Soil, if present, shows its best development near the talus toes, especially on the older mudflow levees. Considerable evidence is available to show that rock­ falls, avalanches, meltwater, and mudflows are the active processes of deposition. Mudflow levees are present on nearly every talus cone (Figs. 20, 21, 22, 44, and 45). Lines 89 painted across cones, to determine amounts of movement, were in numerous places partially destroyed by mudflows. Rock­ falls have been observed to occur where rocks collapsed from cliffs along talus couloirs, fell onto, and rolled down the complex talus cones. Impact pits are present on the talus where large boulders hit and bounced. Avalanches are evi­ denced by debris tails that extend downslope behind large boulders. Debris in the avalanches was deposited at the dis­ tal side of boulders as the avalanche moved downward. Ava­ lanches usually scour a smooth surface on that portion of the cove over which they repeatedly move,

Origin Complex talus cones in the area appear to be the re­ sult of deposition by rockfalls, avalanches, meltwater, and mudflows (Figs. 21 and 22). These processes of deposition appear to shift over the talus cones. Mudflow levees and remnants of levees are positioned over much of the surface (Figs. 21, 22, 44, and 45). Some are recent, others have soil developed in the finer debris. Avalanche and rockfall debris are evenly distributed over the cones. Avalanches, because they move as a mass, bevel and smooth portions of the talus resulting in a smooth surface. It is believed that these four processes were active throughout the time of for­ mation of complex talus cones. Any one process may have been dominant for certain periods. Rockfall was probably most significant during early stages of development until couloirs 90 were established. Avalanches may have been dominant during periods of intensive snow accumulation, such as winter and early spring, whereas mudflows were probably important during more moist times. Mudflows may not have been important until later stages of development after weathering had produced finer material. Freezing and thawing must have been an impor­ tant process in freeing material from the rockwalls and heads of the couloirs. In summary, complex talus cones are thought to be the accumulative product of avalanches, mudflows, melt­ water, and rockfalls.

Fig. 20.— Complex and rockfall talus cones south side Isabelle Valley. Cones A, B, C, and E are com­ plex talus cones. Cone D is rockfall talus. Fig. 21.— Complex talus cone south side Arapaho Valley showing mudflow levees. Note coarse debris in couloir and on lower portion of cone. This cone is the location of motion study 12. Detailed map is Fig. 22. 92

v*S/Vf-

v<

7/ Vy

Mud flow

;v-' Bedrock

Fig. 22.— Detailed map of complex talus cone, shown in Figure 21, on the south side of Arapaho Valley. 9 2 ^ ^ W , / '\ \ * Oj •Q M- i J 0 V > u 3 0 i iv “ , > ■ *- *■ 41 0)4 w J< oo

\ *0 CQ 0 c \ 0 3 0

S' Oj (N o I— ^ 0 1

v y d Xq f O i u a s ; ^ | L O i . p s d jj Avalanche Boulder Tongues

Introduction Avalanche boulder tongue is a term first used by Rapp (1959, P* 34) for an accumulation of rock debris, formed by erosion and deposited by snow avalances. Rapp identified two types, "road-bank tongues" and "fan tongues." Road-bank tongues are elevated and flat topped whereas fan tongues con­ sist of a thin cover of debris that usually extends farther out onto the valley bottom (Rapp, 1959, p. 35). Only the fan tongue type is recognized here in Colorado.

Location Nine fan tongues have been distinguished in the area of investigation (Plate I). Locations are as follows: (1) One on the north side of Arapaho Valley at a position parallel to the downvalley Temple Lake moraine (Figs. 2 3 and 24, and Plate I). (2) Two in Green Lakes Valley, one on the north side of lake No. 1 and facing south, and one on the south side of lake No. 2 facing north (Fig. 11). (3) One in Isabelle Valley, which descends eastward from the north side of Navajo Peak to the cirque floor. (4) One that faces southeast in the small hanging valley half a mile south of Pawnee Pass. (5) Two in Blue Lake Valley, one on the north valley wall north of Blue Lake (Figs. 25, 26, and 27), and one descending northward from an old erosion surface south of Mount Toll to the cirque floor. (6 ) Two at the head of Audubon Valley. They face southeast and extend out onto moralnal material on the valley floor. Description A distinguishing feature of avalanche boulder tongues is the general lack of well-defined continuous couloirs (Figs. 23 and 26). Segments of couloirs are sometimes pres­ ent; however, the source area of the debris on the cliff wall is often large. Numerous small poorly developed couloirs, such as those shown in Figure 26, are often characteristic of the source area. The avalanche boulder tongue shown in Figure 11 has the best developed couloir of any tongue studied. Avalanche boulder tongues in the cirques below Navajo Peak, Mount Toll, and Mount Albion display no couloirs through which debris ladened snow could have been channeled. At some places, bedrock is exposed between the source area and the avalanche boulder tongue (Fig. 26). Longitudinal profiles range from nearly straight (Fig. 23) to concave (Fig. 25). Distal parts of the tongues may reach far out onto the valley floor (Figs. 25 and 27). The avalanche boulder tongue on the north side of Navajo Peak in Isabelle Valley extends down the valley wall, across the cirque floor, and upward approximately 40 feet onto the riegel at the outer lip of this upper cirque. These tongues are fan-shaped, and thin notably toward their distal edges (Figs. 25 and 27). Upper surfaces are usually flat and smooth, giving the appearance of having been beveled. Larger boulders, in some places, extend slightly above the flat surface. Smaller rock debris, carried in the avalances, has collected on the downslope side of the fixed 95 boulders, forming ridges called avalanche debris tails (Rapp, 1959, p. 35). Debris tails are triangular in shape, point downslope, are parallel to each other, range in length from 1 to 25 feet, and vary in widths according to the size of the boulder behind which they accumulate. Debris in the tails is loosely deposited and is commonly oriented in an overlapping imbricate nature. In some cases there are small accumula­ tions of debris on the upslope-side of the fixed boulder, but this proximal tail is smaller than the more characteristic distal tail. According to Rapp (1959, p. 40), the fixed boulder acts as a stopper, and the debris which hits the boulder rolls over it and is deposited on its distal side. The fixed boulder then protects the deposited debris from erosion by succeeding avalanches. Rock debris is angular and shows no appreciable sort­ ing although coarser material has been carried to the edges and even beyond the toe (Fig. 27). Tongues are composed of coarse and fine debris; most bounders are not more than 3 feet in diameter, however, a few are 8 to 10 feet in diameter. Many boulders have been broken during transport as evidenced by their angular shape, freshly broken surfaces, and the scattered distribution of small rock chips over the tongue surfaces. In some places, rocks with elongated axes are oriented with their long axis parallel to the direction of obvious snow movement. A detailed fabric study was not attempted. Debris accumulated by rockfalls and mudflows is 96 common, but the amount contributed is thought to be small. Mudflows and running water may supply small amounts of debris to the proximal part of the tongues (Fig. 26). Scattered plants may occur, although some tongues show little or no vegetation (Figs. 11, 23, 24, and 26).

Origin Avalanche boulder tongues are the result of accumula­ tion, following weathering of rock debris in the source area on the valley wall, and removal and deposition of this debris mainly by snow avalanches. This origin is supported by the fact that avalanche boulder tongues in the valleys studied occur where there is an area suitable for the accumulation of snow and rock debris that is later removed and deposited by snow avalanches. It is the writer's opinion that the source area for the initial accumulation of snow and weathered rock debris is important to the nature of the final deposit. A number of factors pertaining to the source area appear to be vital before an avalanche boulder tongue can accumulate. There must be an area of sufficient size that is susceptible to the drifting and accumulation of snow. Avalanche boulder tongues shown in Figures 11 and 26 have distinct source areas high on the cliff wall; most tongues do not have source areas that are this distinct. However, nearly every avalanche boulder tongue Is associated with a valley wall that lies below an upland surface of notable area. It is the writer's opinion that this upland surface permits the winter westerly 97 winds to drift snow into the source areas. This snow, after excessive accumulation, is periodically released in the form of avalanches, which probably occur during the winter and early spring. The avalanches remove weathered debris from the source area. Debris was probably transported as an occasional boulder in clean snow avalanches and as all sizes of debris in dirty snow avalanches. The smooth rather symmetrical nature of the tongues suggests they were accumulated evenly by piecemeal deposition. Large amounts of debris do not appear to have been deposited at any one time; instead, deposits were probably small, numerous, and rather evenly distributed over a long period of time. Evidence of this is the symmetrical cross profile and the nearly even distribu­ tion of fresh rock debris over the entire avalanche boulder tongue. Fig. 23-— Avalanche boulder tongue, north side Arapaho Valley. Note the absence of well-defined couloirs. Dashed line shows entrance to Henderson Valley which is a hanging valley and an area from which westerly winds may have blown snow that accumulated above the top of the avalanche boulder tongue. Figure 24 is a detailed map of this feature. 99

' -'(X ' ' ' - ' 1 S- >./ t

Mudflow Levees * £ <5? Bedrock

* Vegefotion (stone stripes between rows of vegetotion)

0 10 20 30 ^0 ._i______i_____ Meters

Fig. 2^.— Detailed map of avalanche boulder tongue, north side of Arapaho Valley. Photograph of this tongue is shown in Figure 23. 99

Mudflow Levees

Bedrock

Vegetation (stone stripes between rows of vegetation}

0 10 20 30 40 i— i— i------1----- 1_____ i Meters

Map by

James Richards Fig. 25.— Avalanche boulder tongue, north side Blue Lake Valley showing concave surface and spreading toe.

Fig. 26.— Avalanche boulder tongue, north side Blue Lake Valley, showing large source area for accumulation of debris and snow. Note absence of a couloir. Fig. 27.— Avalanche boulder tongue in center of photograph, north side Blue Lake Valley, show­ ing low angle of toe and the scattering of debris. Fresh rock fragments on glaciated weathered sur­ face in foreground deposited as previous winter's avalanched snow melts. Alpine Mudflows Introduction The type of mudflow In the area studied occurs in an alpine region and may differ from those occurring under humid or arid conditions at lower altitudes. The term alpine mud­ flow is more descriptive and it is this term that Is implied when the word mudflow is used here. Evidence of mudflows Is represented by mudflow levees, especially on talus (Figs. 21, 22, 44, and 45). Behre (1933, p. 634) refers to the mudflow ridges as levees and the associated gullies as ’‘torrential gullies.1' Sharp (1942, p. 222) refers to the gullies as medial channels. Although mudflows are not directly responsi­ ble for the entire deposition of the talus, they are an important process of debris transportation in this alpine region.

Location Mudflows occur on complex talus (Figs. 20, 21, 22, 44, and 45), tops of protalus lobes, avalanche boulder tongues (Figs. 23 and 24), fronts of protalus lobes and rock glaciers (Figs. 6, 12, and 40), and snow banks (Figs. 12, 28, and 29). Evidence of mudflows on talus is extremely common.

Description Levees and associated medial channels are the recog­ nizable evidence of mudflows. Mudflows as well as their associated levees vary considerably in size. Large levees may 103 have a relief of 8 to 10 feet from the crest of the levees to the bottom of the channel, a width of 8 to 20 feet, and a longitudinal extent exceeding 1,000 feet (Pigs. 22 and 24). Some levees can be traced down valley walls, onto, and beyond the distal portions of talus deposits (Figs. 21 and 22). Some levees are built in stages, with debris from succeeding flows overlapping older flows. This is evidenced by buried soils in the levee transverse profile. Rock debris in the levees shows some orientation of the long axis parallel to the direc­ tion of the levees. Rapp (I960, p. 156) determined that "about 50% of the oblong cobbles and boulders were oriented with a deviation of less than 30° from the direction of the levees." Levees are more common on the lower portions of talus. Mudflow debris is characteristic of the distal part of complex talus cones that feed protalus lobes. The mudflow debris accumulates on the back part of the protalus lobes where it builds vertically as well as horizontally onto the lobes by the overlapping of successive flows. The majority of the boulders are 0.5 to 1.5 feet in diameter, 2 to 3 feet diameters are common, and a few boulders are 5 to 6 feet in diameter. Finer material includes sand, silt, and clay sized particles. Mechanical analyses of the finer material indicate a content of 58 per cent sand and nearly 9 per cent silt and clay for particles less than 4 mm. Fine matrix material is characteristic of fresh recent mud­ flows (Figs. 28 and 29) and it is inferred that older mudflows 104 were similar when fresh. Vegetation and soil are common on the older levees, especially those on the distal parts of talus.

Origin Mudflows erode, transport, and deposit rock debris. They appear to occur where abundant fine material, little or no vegetation, and intermittent water supply is characteris­ tic. Behre (1933, p. 635) states they represent the work of mountain torrents produced by concentration of runoff through isolated and narrow couloirs in otherwise unbroken rock walls. Water is supplied during periods of excessive rain or during the time of maximum snow melt; therefore, they are seasonal. Mudflows shown in Figures 28 and 29 occurred in the summer of 1965 after a few days of heavy rainfall. Mud­ flows of notable extent did not occur here during the summers of 1964, considered to be a summer of normal precipitation, or the summer of 1966 which was unusually dry. Mudflows or possibly streams appear to be rather small as they begin on the valley wall. During the early part of their descent, either on the valley wall or higher portions of the couloirs, they erode and pick up rock debris. The early part of the descent is characterized by erosion of a medial channel and deposition of distinct levees (Fig. 12). Evi­ dence of this is supported by the destruction, by mudflows, of motion study lines that were painted across couloirs. Parts of many lines were completely removed while other parts of the 105 lines were buried by the deposition of levees. Sharpe (19^2, p. 222) states that some medial channels are incised 3 to 10 feet below the level of the alluvial surface upon which the levees rest, but others are confined by ridges and are not incised. Deposition of mudflow debris is dominant over erosion by mudflows on the distal portions of talus deposits. This is supported by evidence designated in Figures 12, 21, 28, and 29. In Figures 12, 21, and 29, mudflows were de­ posited on snow with apparently little if any removal of the snow. In Figure 21, deposition of mudflow debris occurs at the lower portion of the complex talus. From the above dis­ cussion, it is obvious that deposition of levees occurs along most of the extent of the mudflows; however, deposition is dominant at the lower parts of talus deposits. It is also obvious from the discussion and from Figures 12 and 21 that a medial channel exists throughout the extent of the mud­ flows, but this channel is mainly erosional on the higher parts of the talus deposits; that is, it erodes into the underlying talus. On lower portions of talus deposits which are also the lower portions of mudflow deposits, channels are also present, but here they have not eroded into underlying talus debris; instead, the channel has been maintained in the mudflow debris due to later flow of the more fluid center of the mudflow. Shapr (1952, p. 222) states, "narrow ridges of un­ sorted bouldery alluvium form levees along channels on alluvial 106 slopes . . . they are built . . . by bouldery streams of mud. Mudflows may follow pre-existing channels or, by moving down undissected slopes, determine the location of new channels confined by the levees and cut by the more liquid part of the flow and the subsequent run-off." Leopold, Wolman, and Miller (1964, p. 342) state, "If the quantity of water In a mudflow is not large, the viscous mass moves downhill, de­ positing a lobate tongue at the foot of the slope." Sharp (1942) maintains that when the flow is more fluid, boulders obstruct the flow by accumulating near the snout. When the moving fluid behind attains sufficient force, the boulders are shoved aside, producing mudflow levees. It must be mentioned that the pronounced nature of the channels is partly attributed to meltwater and rainwater which probably removes debris from the channels. Sharp (1952, p. 226) states, "medial channels are chiefly the product of the later more liquid part of the flow and of subsequent run off. " Mudflows appear to follow channel courses previously established by similar flows or by small channels eroded by meltwater and rainwater. Later mudflows undoubtedly blocked previous mudflow channels which cause still later mudflows to be shifted to other positions on the talus. 107

Fig. 28.— (A) mudflow with some boulder avalanche debris, (B) mudflow, (C) boulder ava­ lanche with some mudflow debris, south side Arapaho Valley south of Arapaho rock glacier.

Fig. 29* Mudflow south side of Green Lakes Valley showing fine fluid material at distal end of flow. 1q 8 Rockfall Talus Introduction Rockfall talus includes ti.o^^talus deposits along the valley walls that have accumulated uue to rockfall. Couloirs may be important (Pig. 51-A), they may be of minor importance (Fig. 51-B and C), or they may be absent (Pig. 31-E). Some debris in the rockfall deposits may be due to snow avalanch­ ing but the -amount is thought to be minor.

Location Rockfall talus is common every side of every valley. Deposits lie at the base of cliffs or perched on small rock ledges where it has accumulated due to free fall of rock debris. These deposits are most common at the base of cliffs between larger complex talus cones (Pigs. 20-D, and 31-E). Major deposits of this type are indicated on Plate I.

Description Rockfall talus deposits that have accumulated as a result of debris moving through either distinct or poorly de­ fined couloirs are usually conical in shape (Pigs. 20-D and 51-A-B-C). Rockfall talus deposited, in absence of couloirs, at the base of steep cliffs is sheet-like (Pig. 31-E). Rock­ fall talus is composed of a larger percent of coarse debris than complex talus cones. Boulders 1 to 5 feet in diameter are most common but boulders up to 12 feet are present. Rock­ fall talus associated with distinct couloirs contain fine 109 material, especially in its upper two-thirds (Fig. 51-A), whereas talus associated with poorly developed couloirs have fine debris only at their apices (Fig. 20-D). Scattered vegetation is present but only on the fine material. The number of large boulders increases toward the bottom of the talus deposits. Slopes are relatively straight and range from 32° to 40° from the horizontal. Impact pits caused by falling, rolling, and bouncing rocks are common on the surfaces. Scattered rock chips suggest shattering due to forceful impact.

Origin Rockfall talus is an accumulation of rock debris that has fallen from valley walls. Material is released by freeze-thaw action and falls over or from steep cliffs or from couloir walls. Material moving through the couloirs may become incorporated into complex talus deposits or develop a rockfall talus cone such as In Figure 51-A. Debris falling over or from a cliff accumulates as a wedge-shaped deposit at the base of the cliff. Joints obviously play an important role in the forma­ tion of couloirs which in turn determine to a large extent the resulting type of talus deposits. From personal observa­ tions, but with no actual count, joints are closely spaced in the area of couloirs. Joints are less closely spaced on the cliff walls and areas above rockfall talus deposits; this has resulted in poorly developed couloirs, a less concentrated 110 source area, and In many places a steep cliff. In summary, the lack of closely spaced Joints Is thought to aid In the formation of rockfall talus. At the same time, less closely spaced joints have permitted freezing and thawing to provide coarse material which is characteristic of the rockfall talus deposits. VOLUME AND DISPLACEMENT OP DEBRIS

Introduction Distances and volumes of debris moved on every feature of mass movement was not attempted. Such measurements were made on selected rock glaciers, protalus lobes, complex talus, and rockfall talus. Selection was determined by distinctness and measurability; for example, the form of mass movement had to be near bedrock on which stationary points were established from which accurate measurements could be made. It should be noted that rates of movement were not obtained for entire features but only for surface debris on them.

Procedures Various procedures were employed for making measure­ ments on different mass movement features. For rock glaciers survey lines were constructed across the rock glaciers by using a plane table and alidade. A permanent alidade station was established on bedrock on one side of the rock glacier; targets were painted on the rock wall on the opposite side; a sight-line was established between the station and a target; shallow holes were drilled in selected boulders on the rock glacier that lay exactly along the sight-line: the holes were ringed with paint, numbered, and plotted on the plane table

111 112 sheet (Fig. 55). Any movement other than parallel to the sight-line was determined from year to year. Debris movement on protalus lobes was measured by three methods. (1) Stationary points on bedrock near the fronts of lobes were established. Holes were drilled on boulders exposed on lobe fronts, a circle was painted around each hole and a number was painted on the boulder. Distances were measured from the stationary point or points on the bed­ rock to the holes drilled in the boulders. Distances between holes were measured and a grid of triangles was established (Fi . 30). By measuring the triangle sides each year and com­ paring them with lengths of previous years, the boulders that moved, relative movement, direction, and approximate distance of movement were determined. (2) Numbers, letters, and figures were painted on boulders exposed on lobe fronts. Photos were taken from an established point on bedrock imme­ diately in front of the protalus lobe. By comparing photos taken each year, relative movement of painted boulders could be determined (Fig. 33)- (3) Distances were measured between marked boulders on the protalus lobe fronts and designated points on bedrock near the lobe front. The distances were measured and compared each year. Movement on talus was determined by two methods. (1) Spikes were driven into bedrock joints on both sides of a couloir, a clothes-line cord stretched from spike to spike, and a straight line was painted beneath the cord on the talus 113 blocks. The following year the cord was stretched from the same bedrock positions to determine any movement of the original line of talus blocks. Each rock that had moved either onto the painted line or away from it was given a number, letter, or figure in order that its movement from one year to the next could be determined (Pig. 41). Distances were measured from the position of the line to the nearest point of contact with paint on the moved boulder. Volumes were determined for each boulder that had moved. (2) A grid sys­ tem of triangles similar to that used on protalus lobes was constructed across some couloirs and rockfall talus. Distances were measured with a steel tape. Distances between holes were measured from center to center, the hole being approximately three-eights to one-half inch in diameter. A year to year difference of .5 cm or less was considered to be a possible measurement error and no movement was recorded. In many Instances, from year to year, some of the painted rocks could not be located or accounted for. For example, a mudflow or avalanche on talus could remove material from certain portions of the painted lines and at the same time deposit new debris on other portions. This resulted in painted debris being burled, scattered, or turned in such a manner that painted surfaces were not visible. It was a dif­ ficult task to turn every rock nearby to discover if its unexposed surface was painted, although a number were located in this way. 114 In the remainder of this chapter, results of motion studies are presented. Triangular grids are reproduced here for future use by others who wish to continue these motion studies. Locations of each motion study and the triangular grids are possible by study of photographs herein and the painted grids at the field locality. Statements for proper understanding of the sketches follow. 1) Letters and numbers on photographs, figures, and Plate I represent positions of individual motion studies. Circled numbers in the figures representing motion studies show positions of individual boulders. 2) Concerning triangular grids, after the numbers are rotated to a reading position, the number on the left is the initial measured distance (most measured in 1965), whereas the number on the right represents the distance measured the following year. If the position of the second number is represented by only a line, no change in distance occurred. 3) Red lines between circled numbers indicate that measurements were not taken prior to 1966. A red line plus a number in a square was also used if the numbered boulders moved considerable distances. 4) When no lines are drawn between circled numbers, an accurate measurement was not obtained. 5) Circled numbers represent rocks on which holes were drilled and numbered. 115 6) Figures representing motion studies are not drawn to scale; instead, numbers, letters, and figures represent relative positions of boulders. 7) Geographic positions of the mass movement features on which motion studies were conducted are indicated by numbers on Plate I. 8) Tinted brown areas in the following figures repre­ sent bedrock. 9) Arrows by the numbered boulders on triangular grids indicate that boulder has moved and also suggests the probable direction of movement. 10) Distances between boulders on the triangular grids are measured in meters and centimeters. Dimensions of boulders and distances of movement on talus surfaces are measured in feet and inches. 116 Blue Lake Valley Motion Study 1-D: This motion study is represented by a tri­ angular grid on the front of the protalus lobe complex on the south side of Blue Lake Valley (Plate I and Pig. 31). Thick­ ness of the protalus lobe at this point is approximately 70 feet; the angle of the front ranges from 39° to A0°.

Fig. 30.— Triangular grid showing results of movement of boulders on front of protalus lobe complex 1-D. 116

Blue Lake Valley Motion Study 1—D: This motion study is represented by a tri­ angular grid on the front of* the protalus lobe complex on the south side of* Blue Lake Valley (Plate X and Pig. 31)- Thick­ ness of* the protalus lobe at this point is approximately 70 feet; the angle of the front ranges from 39° to AO°.

2Q 19

2 3 . - „-i < - i . a j 22] 15.

29. lO

18 13 14

3Q 17. 331

V. 3* - Y . S o a - * * -

Pig. 30. Triangular grid showing results of movement of boulders on front of protalus lobe complex 1—D. 117

Pig. 31.— Protalus lobe complex and talus, south side Blue Lake Valley, south of Blue Lake. Letters represent positions of motion studies; A and B on complex talus; C, D, and X on protalus lobe complex; and E on rockfall talus. This talus complex is No. 1 on Plate I. 118

TABLE 5* Dimensions and Volumes of Boulders Involved in Motion Study 1-D.

Boulder Dimensions Volume Boulder Dimensions Volume No. (inches ) m 3 No. (inches) I n5 1 41x30x15 18,450 17 20x19x13 4,940 2 66x53x15 52,470 18 21x14x11 3,234 3 81x51x24 99,144 19 24x 9x13 2,808 18x10x10 1,800 20 60x43x48 123,840 5 32x28x10 8,960 *21 24x15x9 3,240 6 28x20x14 7, 840 22 42x25x11 11,550 7 26x10x23 5,980 *23 16x13x17 3,536 *8 19x21x11 4,389 24 29x17x14 6,902 9 13x12x19 2,964 25 21x27x 6 3,402 *10 17x14x11 2 ,618 26 33x18x14 8,316 *> 11 13x14x15 2,730 27 19xl7x? • *12 24x 9x11 2,327 28 27x17x11 5,049 *13 56x35x63 123,480 *29 19x17x13 4,199 *14 20x29x15 8,700 30 95x99x36 339,580 *15 34x12x12 4,896 31 17x18x10 3,060 16 l8xllx 8 1,584 32 19xl6x 6 1,824 Boulders that moved. Total volume involved 873,812 in.3 Total volume moved from 1965 to 1966 159,185 in.^

Motion Study 1-C: This motion study is based on a triangular grid constructed on the front center of the protalus lobe complex shown in Figure 31* The angle of the front varies from 36° to 39°. 119

Fig. 32.— Triangular grid showing results of move­ ment of boulders on front of protalus lobe 1-C. 12 0

TABLE 6. Dimensions and Volumes of Boulders Involved in Motion Study 1-C.

Boulder Dimensions Volume Boulder Dimensions Volume No. (inches) in3 No. (inches) in3 1 144x225x102 3,304,800 10 20x26x 8 4,160 2 39x 54x 36 44,712 11 17xl6x 5 1,360 3 3 8 x 3 4 x 21 27,132 12 54x27x22 32,076 4 4lx 3 8 x 13 20,254 *13 22x18x14 5,544 5 32x 29x 13 12,064 14 45x45x29 58,725 6 23x 22x 4 2,024 15 29x25x 9 6,525 7 l8x 22x 10 3,960 *16 22x20x20 8,800 8 22x 17x 23 8,602 17 12x45x20 10,800 9 22x 26x 16 9,152 18 72x20x48 69,120 *Boulders that moved. Total Volume Involved 3)629,810 in.3 Total Volume Moved from 1965 to 1966 14,344 in.

Motion Study 1-X: This is a motion study based on photo­ graphs of the front of the upvalley lobe of the protalus lobe complex shown in Figure 31-X. Photographs were taken In 1965 and 1966 of painted rocks on the lobe front but no notable movement was observed during this one year interval. Figure 33, a photograph of the front, Is included here as a compara­ tive photograph for anyone wishing to see if and when this portion of the lobe does move. Motion Study 1-A: This motion study is on a complex talus above the protalus complex shown in Figure 31. Two types of movement studies were applied. First, a straight line was painted across talus high In the couloir (Fig. 34-1 and Table 7). Second, a triangular grid was constructed across the couloir at a lower position (Fig. 34-2 and Table 8). The talus has a rather small source area and does not reach to 121

Fig. 33-— Photo (August, 1965) of painted debris on front of upvalley lobe of protalus lobe complex south side of Blue Lake Valley. Location is No. 1 on Plate I and point X in Figure 31.

1) Painted Line

2) Triangular Grid.

Fig. 3^.— Results of debris movement at (J.) painted line and (2) triangular grid constructed across complex talus 1-A. 122

TABLE 7. Movement and Volumes of Boulders Involved in Motion Study 1-A, Pig. 35-a.

Letters on Distance Dimensions of Volume of Moved Boulder Moved Boulders (Inches) Boulders X onto line 6x6x8 288 I v 8x5x2 80 A 11 6” 4x4x5 80 T 12'6" 12x9x5 540 Total Volume Moved from 1965 to 1966 988 in. 3

TABLE 8. Dimensions and Volumes of Boulders Involved in Motion Study 1-A, Fig. 35-b.

Boulder Dimensions Volume Boulder Dimensions Volume No (inches) (In3 ) No. (inches) (ln3) 1 48x85x44 179,520 9 27x24x 8 5,18*1 2 34x29x 8 7,888 10 I4x 5x ? ? 3 10xl9x 6 1,140 11 38x30x24 27,360 4 23x29x10 6,670 12 bedrock *5 17xl6x 5 1,360 13 24x24x 7 4,032 *6 21x24x3 1,512 14 44x16x20 14,080 7 bedrock *15 43x20x29 31,320 8 105x94x58 572,460 16 bedrock *Boulders that moved. Total Volume Involved 852,526 i n . 3 Total Volume Moved from 1965 to 1966 34,192 i n . 3 the top of the valley wall. This may account for the small amount of movement that was recorded. The slope ranges from 27° at the base to 40° at the positions of the motion study. 123 Motion Study 1-B: This motion study Is represented by a tri­ angular grid across a complex talus shown in Figure 31. The slope of the talus is 32°. See Figure 35 and Table 9.

Fig. 35.— Triangular grid showing results of movement of boulders on complex talus 1-B.

Motion Study 1-E: This motion study is a triangular grid constructed in 1965 on rockfall talus at location E, Figure 31. Measurements in 1966 showed that no movement had occurred (Fig. 36). 123 Motion Study 1-B: This motion study is represented by a tri­ angular grid across a complex talus shown in Figure 31* The slope of the talus is 32°. See Figure 35 and Table 9*

Fig. 35.— Triangular grid showing results of movement of boulders on complex talus 1-B,

Motion Study 1-E: This motion study is a triangular grid constructed in 1965 on rockfall talus at location E} Figure 31. Measurements in 1966 showed that no movement had occurred (Fig. 36). 124

TABLE 9* Dimensions and Volumes of Boulders Involved in Motion Study 1-B

Boulder Dimensions Volume Boulder Dimensions Volume No. Cinches) (m3) No. (inches) (in3) 1 36x28x16 16,128 16 41x45x28 51,660 *2 32xl8x 6 3,096 17 60x37x21 46,620 *3 12x28x28 9,408 18 35x70x15 36,750 *4 l6x25x 9 3,600 19 20x24x15 7,200 5 34x38x ? 0 20 42x55x14 32,340 *6 31x31x11 10,571 21 26x26x31 20,956 7 24x18x7 3,024 22 28x33x17 15,708 8 86x95x34 277,780 *23 15x19x12 3,420 *9 38x35x12 15,960 24 35x21x11 8,085 10 31x26x15 12,090 25 33x31x21 21,483 11 34x32x16 17,408 26 47x36x25 42,300 12 50x36x13 23,400 27 76x53x48 193,344 *13 48x18x21 18,144 *28 12x26x31 9,672 *14 26x30x15 11,700 *29 20x18x19 6,840 15 38x25x18 17,100 1 Boulders that moved. Total Volume Involved 935,787 in.3 Total Volume Moved from 1965 to 1966 92,411 in. 3

Fig. 36.— Triangular grid showing results of movement of boulders on rockfall talus 1-E, Figure 31. 125 Motion Study 2: This motion study is on rockfall talus lo­ cated at No. 2 on Plate I and point A in Figure 16. The slope angle is 37° at the position of the triangular grid. See Table 10 for movement results.

Fig. 37*— Triangular grid showing results of movement of boulders on rockfall talus 2.

TABLE 10.— Dimensions and Volumes of Boulders Involved in Motion Study 2.

Boulder Dimensions Volume Boulder Dimensions Volume No. (Inches) (in3) No. (inches) (in3) *1 33x31x20 20,460 10 46x30x24 33,120 2 47x34x18 28,764 11 15x24x12 4,320 *3 37x25x 9 8,325 12 45x28x16 20,160 4 50x32x11 17,600 13 21x22x10 4,620 5 33x17x20 11,220 14 21x26x17 9,282 6 48x50x24 57,600 15 16x21x10 3,360 *7 40x22x14 12,320 16 31x26x10 8,060 8 26x30x 9 7,020 17 33x28x12 11,088 9 14x20x20 5,600 Boulders that moved. Total Volume Involved 262,919 in.3 Total Volume Moved from 1965 to 1966 41,105 in.3 126 Isabelle Valley Motion Study 3-A: This motion study is based on a triangular grid constructed on the upvalley lobe of the protalus lobe complex shown on Plate I and Figure 40. Boulder sizes were not obtained. The motion study is shown in Figure 38.

Motion Study 3-B: This motion study Is based on a triangular grid constructed on the downvalley lobe of the protalus lobe complex shown In Figure 40. Boulder sizes were not obtained. The protalus lobe is approximately 35 feet thick and has a slope at Its front at 42° to 44°. The motion study consists of a triangular grid shown in Figure 39.

Motion Study 3-C: This motion study is based on a single line painted across complex talus (Fig. 41) in the upvalley couloir behind the protalus lobe complex in Figure 40. The angle of talus accumulation is 39°. See Table 11 for dis­ tances of movement and volume of debris moved.

Motion Study 3-D: This motion study is based on a single line painted across complex talus (Fig. 42) in the downvalley couloir behind the protalus lobe complex in Figure 40. The slope angle is 33° at the point where the line crosses the talus. See Table 12 for distances of movement and volume of debris moved. 127

/

Fig. 38.--Triangular grid showing results of movement of boulders as protalus lobe 3-A. 128

Pig. 39.— Triangular grid showing results of movement of boulders on front of protalus lobe 3-B. 129

Pig. 40.— Protalus lobe complex and talus, south side Isabelle Valley. This location is No. 3 on Plate I. Letters represent positions of motion studies: A and B on protalus lobe front, C and D on complex talus. Items to note: (1 ) mudflows and debris across snow at lobe front, (2 ) coarse upper surface, (3) three major lobes, (4) snow­ banks at front and In depressions, (5) 0 is position of spring that emerges at lobe front. 130

34

Fig. 41.— Results of motion study based on line painted across complex talus 3-C.

B

Fig. 42.— Results of motion study based on line painted across complex talus 3-D. TABLE 11. Movement and Volume of Boulders Involved in Motion Study 3-C.

Letters Movement and Total Dimensions Volume Movement Dimensions Volume Numbers 64-65 65-66 64-65 (inches) (m3) Numbers 65-66 (inches) (in3) • 1'2" 3'3" 415" 6x3x1.5 27 10 l4xl0x 7 980 A 8 * 1 '6" 9 1611 12x9x 3 324 11 8x13x7 273 B 7'6" 11411 8'10" 12x5x 4 240 12 17x 7x4 476 C 7,7, 1* 3" 8' 10" 12x19x8 1,824 13 611 8x11x10 880 D 8’10" 2" 9' 12x19x8 1,824 14 6" 22xl2x 6 1,584 E 8*4" 40' 48' 4" 29x11x16 5,104 15 5" buried F 8'6" 4" 8'10" 9x12x11 1,188 16 5" 8x 7x 5 280 G 515" 9" 6 ' 2" 73x20x22 32,120 17 23x11x10 2,530 H 11' 6" lost 7 18 19xl7x 9 2,907 I 3.5" 6.5" 10" 12x12x15 2,160 19 1011 12x12x15 2,160 J 4'9" 1*5" 6 '2" 17xl6x 7 1,904 20 6x 6x 4 144 K 1.5" lost 7 21 2.8" l8x 9x 6 972 0 13’10" 6" 14*4" l4xl2x 5 840 22 17x14x18 4,284 V 6’ l'l!l 711" 2x 6x 2 36 23 llx 4x 8 352 X 8’ 2 ' 10' lOx 9x 5 450 24 buried 7 Y 8*9" 5" 9'2” 19x 9x 5 855 25 8x 9x 8 576 1 — 10*' 10" 4x 6x 3 72 26 llx 7x 6 462 2 llx 8x 7 616 27 9xl7x 6 918 3 -- 9.5" 9-5" 39x20x14 10,920 28 55x30x24 39,600 — 4 5-5" 5.5" 17x17x20 5,780 29 __ , 34x20x24 16,320 5 10xl8x 5 900 30 2 1 lOx 7x 5 350 6 — 4" 4” 22x12x12 3,168 31 3,5ii 25x10x11 2,750 7 --- 5" 5" 15x 5x10 750 32 3'5" 17x 7x11 1,309 8 --- 5" 5" l4x 9x 5 630 33 3' 15xl8x 8 2,160 9 — 5" 5" I4x 9x10 1,260 35 24110" 20x10x11 2,200 No movement. Boulders moved onto line. Total Volume Moved from 1964 to 1966 157,459 in.3 TABLE 12. Movement and Volume of Boulders Involved in Motion Study 3-D.

Movement Dimensions Volume Movement Dimensions Volume Letters 64-65 65-66 Total (inches) (in3) Numbers 65-66 (inches) (in3) A 311)it 2 " 3f 6n llx 5x 3 165 1 3” 5x 7x 1 35 B 7 •8" 8" 8 '4" 13x 6x 2 156 2 rotated 13x 5x 3 195

C 3" — 3" 17xl8x 8 2,448 3 4ir 7x 4x 3 94 I 8” — 8:’ 4x 4x 8 128 4 7" 7x 3x 4 94

J 1*9" — I19" 13xl4x 8 1,456 5 2" 9x 4x 3 106 M 12’10" 3” 1311" 5xl0x 7 350 6 1.5" llxlOx 7 770

0 7" — 7" 6x 4x 1 24 X 3* 3' 4x 4x 6 88 No movement. Total Volume Moved from 1964 to 1966 6,109 in.3. 133 Motion Study 4 : This motion study is based on a triangular

grid constructed across the complex talus cone in Figures M

and 45, The volume of movement is shown in Table 13 and the

triangle grid is shown in Figure *13.

Pieces

22 & 23

Fig, 43.— Triangular grid showing movement of rock debris at motion study on complex talus cone *1, Boulder No. 22 was broken into many pieces. Numbers in squares show new location of boulders after movement. 134

Fig. 44.— Complex talus cone north side Isabelle VaAley, position 4 on Plate I. Relief from talus toe to top of cliff Is approximately 1,200 feet. Figure 45 is a detailed map of this talus. Hatch marks indicate area of motion study 4. 135 A / ■>

w

iow Levees Bedroc k Trail -V Vegetation

tA ete rs

Map by James Richards

Fig. 45.— Detailed map of complex talus cone shown in Figure 44. 136

TABLE 13. Dimensions and Volumes of Boulders Involved in Motion Study 4.

Boulder Dimensions Volume Boulder Dimensions Volume No. (inches) (in^) No. Cinches) (m3)

4 33x27x 8 7,128 14 1 6 x 1 3 x 6 1,248 5 23xl8x 9 3,726 *15 36x12x14 6,048 6 17x14x10 2,380 16 72x34x14 34,272 7 24x11x18 4,752 17 40x64x20 51,200 8 31x22x18 12,276 *18 31x27x16 13,392 *9 31x12x13 4,836 *19 140x78x42 45,864 *10 28x30x20 16,800 20 43x42x26 46,956 *11 32x29x10 9,280 *22 28x31x42 36,456 *12 14x15x16 3,360 *13 31x13x11 4,433 "5f------Boulders that moved. Total Volume Involved 304,407 in.3 Total Volume Moved from 1965 to 1966 144,195 in.-^

Pawnee Valley Motion Study 5-A^: This motion study is based on a triangular grid established on the west lobe of the bilobate protalus lobe shown in Figure 47. Dimensions of every boulder was not obtained. The slope of this position is 39° to 4l° . 137

Fig. 46.— Triangular grid showing results of movement of boulders on front of protalus lobe 5-A. Fig. 47.— Protalus lobes, north side of Pawnee Valley, position No. 5 on Plate I. Letters indicate positions of motion studies. 0 is the position of a spring that emerges at the lobe front. 139

TABLE 14. Dimensions and Volumes of Boulders Involved in Motion Study 5-A.

Boulder Dimensions Volume Boulder Dimensions Volume No. (inches) (in3) No. (inches) (in3) *7 34x14x11 5,236 *18 17x30x8 4,080 *8 13x26x12 4,056 *19 34x18x13 7,956 *12 31x26x11 8,866 *20 16x11x15 2,640 *13 22x20x12 5,280 *21 15x18x13 3,510 16 16x24x11 4,224 *Boulders that moved. Total Volume Moved from 1965 to 1966 45,848 in.3

Motion Study 5-B: This motion study is represented by a triangular grid similar to 5-A except it is on the front of the east lobe of the bilobate protalus lobe in Figure 47. The slope of this location Is approximately 46°.

TABLE 15- Dimensions. and Volumes of Boulders Involved. in Motion Study 5-B.

Boulder Dimensions Volume Boulder Dimensions Volume No. (Inches) (in 3) No. (inches) (in 3) 1 27x20x15 8,100 *11 28x19x10 5,320 2 47x30x23 32.430 *12 I8xl3x 8 1,872 3 30x20x12 7,200 *13 26x21x 8 4,368 4 30xl4x 7 1,470 14 20x12x11 2,640 5 21xl4x 8 2,352 *15 35x19x14 9,310 6 20xl7x 7 2,380 *16 49x36x24 42,336 7 25x22x17 9,350 *17 23xl9x 6 2,622 *8 24x20x18 8,640 *18 23x13x12 3,588 9 27xl9x 8 4,104 *19 61x40x27 65,880 10 25xl6x 7 2,800 20 13xl0x 5 650 * Boulders that moved. Total Volume Involved 217,412 in.3 Total Volume Moved from 1965 to 1966 146,288 in.3 140

• L i - 0 3

So.

Fig. 48.— Triangular grid showing results of movement of boulders on protalus lobe 5-B. 141 Green Lakes Valley Motion Study 6-A: This motion study was made on the front of a protalus lobe, south side of Green Lakes Valley and Green Lake No. 5 (Plate I and Pig. 50). Holes were drilled on boulders on the lobe front from which distances were measured to select reference points established on bedrock on the valley floor near the front of the protalus lobe (Pig. 49). Distances of movement are shown in Table 20.

.OK

v

6K

2K 5 K SNOW 3K 4K

Pig. 49.— Motion study constructed on front of bilobate protalus lobe south side of Green Lakes Valley south of Green Lake No. 5 (Plate I and Pig. 50). Numbers and letters indicate positions of holes drilled on boulders. This study was made by S. E. White. 1HZ

Fig. 50.— Protalus lobe, Green Lakes Valley, south of Green Lake No. 5. Numbers represent positions in couloir where lines were painted. This is position 6 on Plate I.

Fig. 51.— Rockfall talus cones south side Green Lakes Valley and Green Lake No. 5. A) is rockfall talus cone in­ cluded in motion study 7. A) is a rockfall talus with def­ inite couloir. B and C) are rockfall talus with nondistinc- tive couloirs. 143 Motion Study 6-B: This motion study Is on a complex talus in the couloir that supplies debris to the protalus lobe south of Green Lake No. 5 (Plate I and Fig. 50). Four lines were painted across the couloir (Figs. 50 and 52). Slopes of the talus debris are 35° at line 1, 28° at line 2, 33° at line 3, and 37° at line 4. See Tables 16, 17, 18, and 19 for dis­ tances and volumes of movement of debris onto and away from respective lines. Line 1 (highest).

8 6 - 9 - 9 -

Line 2.

Line 3 *

Line ii (lowest)* /.til * 4-yWyr ?£--- U03----U 2 - 2 U 5 J © 11

9 1 * * » 10 Fig. 52.— Relative positions of rock debris that has moved onto or away from lines painted across complex talus 6-B. 144

TABLE 16. Dimensions and Volumes of Boulders Involved in Motion Study 6-B, line 1.

Boulder Dimensions Volume Boulder Dimensions Volume No. (inches) (in3) No. (inches) (m3)

1 12x 8x 6 57 6 ■ 3x4x1 12

2 17x 9x 4 612 • * 5x4x.5 10

3 17xl0x 8 1,360 * * « 4x4x4 64

* • 4 lOx 5x 3 150 * * 3x6x2 36

• 5 29x21x 6 3,654 * * 3x3x1.5 13.5 6 5x 3x 3 45 Total Volume Moved 6,532.5* No. 1 was the only boulder to move between 1964 and 1965 during which time it moved 31 inches from the line. The remaining boulders moved onto the line between 1965 and 1966.

TABLE 17* Movement and Volume of Boulders Involved in Motion Study 6-B, line 2.

Boulder Movement Dimensions Volume No. 64-65 65-66 Total (inches) (in3) 1 6" 6" 1' 7x 8x 4 224 2 3" 311 13x 7x 6 546 3 1' 3,! -- l r3” 17x27x17 7,786 4 13x15x14 2,730 5 12xl6x 7 1,344 Movement 66 6 25x12x12 3,600 7 13xl3x 7 1,183 8 12x 8x 6 576 9 9x 4x 4 144 10 7x 7x 8 392 No movement. Movement onto painted line. Total Volume Moved from 1964 to 1966 18,525 in.3 TABLE 18. Movement and Volume of Boulders Involved In Motion Study 6-B. line 3.

Boulder Movement Dimensions Volume Boulder Movement Dimensions Volume No. 64-65 65-66 Total (inches) (in3) No. 64-65 65-66 Total (inches) ( i n h 1 8x 5x 4 161 11 -- 51' 7x 7x 3 147 2 8xl7x 4 544 12 3" 3" llx 9x 5 495

------3 5x12x12 720 ■ -- 2" 4x 2x 2 16

4 ------l6x 4x 3 192 * * ------6x 3x 2 36

5 8,: 8” 12xl4x 3 504 • • « 3" 3,; l6xl0x 6 960

• • 6 -- 8" 12x 8x 3 288 « # 2.51: 2.5;: 4x 4x 2 32

* * * 7 9x 6x 2 108 • 9 31' 3,: 8x 4x 7 224

8 4" 4H l6x 7x 5 560 V 6x 4x 2 48

9 3” 3” 9x 5x 2 90 r ------4x 2x 2 16

10 3" 3" 9x 6x 3 81 + -- 2.5;! 6x 6x 2 72

Z 2.5” 7x 6x 3 63 No movement. Moved onto line. Total Volume Moved from 1964 to 1966 5,356 in.^ TABLE 19. Movement and Volume of Boulders Involved in Motion Study 6-B, line

Movement Dimensions Volume Movement Dimensions Volume Boulder 64-65 65-66 Total (inches) (In3) Boulder 64-65 65-66 Total (inches) (m3) 1 rotated 12x 5x 3 180 N 3x 3x 7 63 2 l'l" -- l’l" 12x 8x 2 192 0 -- 9x 4x 4 144 3 3' 8" l'! 3’9': 9x 6x 4 216 P 12x 4x 5 240 4 rotated l6xl3x 7 1,456 Q -- 4x 4x 3 48 5 5" 4" 9" 6x 7x 3 126 R -- 6x 4x 2 48 6 -- 9x 5x 4 180 S ,—__ -- - lOx 9x 3 270 7 — l6xl0x 7 1,120 T -- 2 ‘" 2" 4x 6x 2 48 8 4” — 4” 18x19x10 3,420 U -- 1r 3" 1*3" 4x 2x 1 8 9 15’1011 i'll" 17' 9" lOx 3x 3 90 V -- 4" 4” 5x 5x 3 75 10 -- 57' 4" 57 ’4" 9x 7x 4 252 W -- 4x 4x 1 16 11 -- 2' 2 T 7x 5x 3 105 X „— -- 2x 2x 4 16 12 -- llx 5x11 605 Y -- 7" 7:! 7x 3x 2 42 13 -- 9x 9x 5 405 Z -- 6” 6" 6x 4x 4 96 14 -- 5x 4x 4 80 # 4x 2x 2 16 A — — — 7'3" 7' 3" llx 6x 5 330 0 -- 2' 2i( 2 1 2" 2x 4x 1 8 B -- 6" 6" 7x 3x 3 63 • • • -- I'll" n r 1 5x 3x 2 30 C lOx 6x 4 240 * * • • -- 1' 8" 1' 8" 5x 4x 3 60 D -- 4x 3x 1 12 • • *• —_ 9" 9” 5x 3x 3 45 E --- 5x 4x 1 20 •* • --- 40' 40' 4x 6x 120 i * 5 F 5x 6x 3 90 10'3" 6" 10 T9" 7x 4x 2 84 G --- 4" 4«» 9x 6x 4 216 + 7x1.5x2 21 H 7x 5x 4 140 A ___ 4x 3x 2 24 I --- 4x 3x 5 60 + 4” 4" 4x 4x 2 32 J --- 5" 5" 4xl0x 5 200 * 5x 4x 3 60 K -r — — 9f! 9" 8x 5x 2 80 ? — 28' 71' 28' 7" 3x 3x 1 9 L 2" 6x 4x 2 48 A --- 5x 4x 3 60 M 4" 7x 2x 3 42 No movement. Moved onto line. Total Volume Moved 11,651 in.3 147 TABLE 2 0. Movement on Protalus Lobe, Motion Study 6-A

Movement (cm) Movement (cm) Boulder 64-65 65-66 Total Boulder 64-65 65-66 Total OK 2.5 cm 4K 1.5 2 3.5 IK 2 1 3 5K 3 2 5 2K -- 1 1 6K 2 3 5 3K .5 .5

- --No movement. Average Movement 1.46 cm/yr.

Motion Study 7: This motion study was made on a rockfall talus cone, south side of Green Lake No. 5 (Plate I and Fig. 51-A). Five lines were painted across the talus, which has a slope of 44° to 45°. This study was constructed and main- tained by S. E. White from 1964 to 1966. Numbers and positions of moved debris were not obtained; instead, the volumes were recorded (Table 21).

TABLE 21. Volume of Debris Moved on Motion Study 7*

Line No. Volume of debris moved 1 (highest) 54,595 cm3 3333 in3

2 29,768 1818 in3 3 60,014 3664 in3 4 133,760 8166 in3 5 (lowest) 30,326 1851 in3 Total 308,483 cm3 18,833 in3 10,893 ft3 148 Motion Study 8: This motion study was made on a rockfall talus cone on the north side of Green Lake No. 5 (Plate I and Pig. 51). Three lines were painted across the couloir (Figs. 51 and 53)* Slopes of the talus debris are 35° at line 1, 40° at line 2, and 40° at line 3- See Tables 22, 23* and 2 4 for distances and volumes of movement of debris onto and away from respective lines.

Line 1 (highest).

Line 2L

8 ...

Line 3 (lowest).

20

Fig. 53*— Relative positions of rock debris that moved onto or away from lines painted across rockfall talus cone 8. 149

TABLE 22. Movement and Volume of Boulders Involved in Motion Study 8 , line 1.

Movement Dimensions Volume Boulder 1965-66 (inches) (in3 ) A rotated 6x 4x 2 48 B I4x3x 5 210 C 1*4" 15x9-5x5.5 784 D 7x 5x 1 35 E lOxlOx 3 300 F 17x 9x 8 1,224 G 5x 7x5.5 193 H 6x 4x 6 144 I l6xl5x 6 1,440 J 6 " I4xl2x 8 1,344 A rotated 2x 6x 2 24 * • * 3" 4x 2x 3 24 -- Moved onto line. No movement occurred during 1964-65 period. Total Volume Moved from 1965 to 1966 5770 in, 3

TABLE 23. Movement and Volume of Boulders Involved in Motion Study 8, line 2 •

Movement Dimensions Volume Boulder 1965-66 (inches) (in 3) 1 ---- 6x 5x1.5 45 2 9x 6x 4 216 3 8x 5x 4 160 4 8x 6x 4 192 5 ---- 5x 3x 2 30 6 llx 6x 4 264 7 l ’l" 12x 7x 5 420 8 2*4" 19xl6x 7 2,128 9 1' 4x 6x 5 120 10 2" 9x 7x 4 252 1* 3x 2x1.5 9 I’ll" 4x 3x 2 24 --- Moved onto line. Total Volume Moved from 1965 to 1966 3860 in.3 TABLE 24. Movement and Volume of Boulders Involved in Motion Study 8, Line 3*

Movement Dimensions Volume Movement Dimensions Volume Boulder 65-66 Total (inches) (in3) Boulder 64-65 65-66 Total (inches) (in3 )64-65

1 — _ — 3" 3" 19xl0x 8 1,520 B 14 12” _ _ _ 1412" 16x13x12 2,496 2 — — — 2" 2" l6xl6x 6 1,536 C 6" MM — 6" 6x 4x12 288 3 ------4" 4" 16x18x14 4,032 D ------8x 6x 9 432 4 ------6" 6" 21x12x10 2,520 0 5" ------5" 8x 4x 4 128

5 MM 2" 2" I4xl3x 6 1,092 T 5 u — — — 5" 3x 2x 4 24 6 ------1»1,t l'l" 12xllx 8 1,056 X ------5x 8x 6 240 7 M— — 5" 5" 7x 6x 4 168 Y ------5" 5" 9x 5x 2 90 8 7x 5x 5 175 Z 2 11 6x 4x 4 96

10 w m mm 2” 2" 8x 5x 3 120 20 2" 6x 7x 3 126

—----- 11 6x 4x 4 88 » 3" 6x 4x 3 72 ------12 7x 6x 4 168 • * 1.5 4x 2x 2 16 « • 13 llx 8x 7 616 • 7x 3x 4 84

• • 14 8x 6x 4 192 • • 6x 5x 3 90 15 ------3TT 3" 5x 4x 5 100 --- 3” 7x 4x 2 56 16 9x 5x 3 135 m 5" --- 5" 3x 2x 6 36 17 lOx 4x 5 20

No movement, moved onto line. Total Volume Moved 1964 to 1965 17,992 in.3 151 Motion Study 9 : This motion study was made on a rockfall talus that supplies debris to a small protalus lobe on the south side of Green Lakes Valley (Plate I and Fig. 12). The slope angle is 36° at the position of the triangular grid.

■"^25___-

«L

Fig. 54. Movement of debris shown by a triangular grid constructed across rockfall talus 9.

TABLE 25. Dimensions and Volumes of Boulders Involved in Motion Study 9.

Dimensions Volume Dimensions Volumes Boulder (Inches) (in3) Boulder (inches) (in^) *1 440x24x12 126,720 9 252xl7x 8 2,016 *2 24x48x22 25*344 10 32x26x11 9,152 3 l8xllx 8 1,584 11 56x58x20 64,960 4 22x21x 9 4,158 *12 30xl5x 7 3,150 *5 98x96x28 263,424 13 25x 8x13 2,600 6 20x33x 9 5,940 14 26xl5x 7 2,730 7 19x24x11 5,016 *15 92x20x13 23,920 8 25x28x 7 4,900 *16 41x36x16 23,616

Boulders that moved. Total Volume Involved 569*2 30 Total Volume Moved 466,174 in.3 152

Arapaho Valley Motion Study 10: Results of this study are based on survey

lines across the Arapaho rock glacier. Only distances, directions, and positions of surface boulder movement are given here. Boulder sizes are not yet obtained. This move­ ment study was initiated in 1961 under the supervision of

S. E. White.

6Q5 J 7.5

Survey J Line* \ Plane Table k l Station

Pig. 55.— Motion study 10 constructed on Arapaho rock glacier at the head of Arapaho Valley. Numbers indicate total movement in cm from 1961 to 1966. Arrows show the directions in which the marked boulders moved. Each point represents a marked boulder that lay on the initial survey line. 153

Motion Study 11: This motion study was made on a complex talus on the south side of Arapaho Valley, 100 yards south­ east and downvalley from Arapaho rock glacier (Plate I). Three lines were painted across the talus (Pig. 56). The talus debris has a slope of 38° at line 1, 4o° at line 2, and 40° at line 3. See Tables 26, 21, and 28 for distances and volumes of movement of debris onto or away from motion lines. Line 1 (highest).

V g ~x---- <6Ca pH W" <£> Z OT F W El R

16 J

19

Line 2

3

4

Line 3 (lowest)

3 1 IS L 1 6. Z Fig. 56.— Relative positions of rock debris that moved onto or away from lines painted across complex talus 11. TABLE 26. Movement and Volume of Boulders Involved in Motion Study 11, Line 1.

Movement Dimensions Volume Movement Dimensions Volume Boulder 64-65 65-66 Total (inches) (m3) Boulder 64-65 65-66 Total (Inches) (inJ) 2 7x 3x 5 105 J 56 * 711 2' 7" 59' 2" 6x 9x 6 324 3 1.5 lOx 6x 7 420 K — _ 12x 3x 6 216 4 4 12xl0x 5 600 L 7x 6x 4 168 5 5 7x 8x 4 224 M 13xl4x 5 910 6 4x 5x 2 40 N 6xl0x 4 240 7 —_ 30x22x17 11,220 0 11" 1" 12" 3x 3x 4 36 9 -- lOx 4x 4 160 P 4x 4x 3 48 10 -- 5x 6x 3 90 Q 24 llx 6x 9 594 11 — 7x 6x 3 126 R 23' 8U -- 15x 7x12 1,260 12 -- 8xl0x 4 320 T l’l" 1" 1 * 2 3x 5x 2 30 13 — 4xl2x 5 240 U 50' 10xl7x 9 1,530 14 —— 4x12x10 480 V 3.5 .5 4" 3x 3x 3 27 15 —— 12x 7x 6 504 W 519" -- 8x 3x 2 48 16 8x 7x 5 280 X 9.5" 3x 5x 2 30 17 8x 8x 6 384 0 41 7.1 lost 8x 8x10 640 18 -- 6 1 ' H" 9x 5x 6 270 Y 7x 6x 2 84 19 -- 135' 135' 12x 5x 4 240 Z 15" 2" 17" lOx 4x 3 120 A -- llx 7x 3 231 * 8 4x 3x 2 24 B 5x 4x 8 160 o 4x 4x 2 32 C 4" 4" 8x 8x 6 384 • » • « -- 4x 2x 3 24 D 6x 6x1.5 54 74" -- 4x 3x1.5 18 E llx 9x 9 891 □ 3" 6x 9x 5 270 F 12" 5x 7x11 385 CP 13.5 2.5 16 4x2.5x3 30 G 15xl5x 6 1,350 4 5" -- 5" 4x 3x 3 36 H 1" lost 15x 5x 5 375 3 34 lost 2x 2x 1 4 I 12x 8x11 1,056 8 17x11x11 2,057 Moved onto line, No movement. ~ Total Volume Moved from 1964 to 1966 29,405 in.-* TABLE 27. Movement and Volume of Boulders Involved in Motion Study 11, Line 2.

Movement Dimensions Volume Movement____ Dimensions Volume Boulder 64-65 65-66 Total (inches) (in3) Boulder 64-65 65-66 Total (inches) (in^)

1 11" 1" 12" 6xl0x 4 240 10 29x16x10 4,650

2 6 — l6x 9x 6 486 11 4" 9x 4x 5 180

3 14' 9" 4” 15'3” 5*5x 5x 6 16'5 * LJ , 1 3" 4x 2x 2 16

4 54' 1Q,! 54!10” 7x11x2.5 192 * * 1.5” 6x 6x1.5 54

8 lOx 5x 5 250 t 1 » 3” 8x 4x 5 160

9 9x15x10 1,350 • • • • 5x 2x 5 50

No movement, Moved onto line. Total Volume Moved from 1964 to 1966 7,783 in.3 TABLE 28. Movement and Volume of Boulders Involved in Motion Study 11, Line 3.

Movement Dimensions Volume Movement Dimensions Volume Boulder 64-65 65-66 Total(inches) (in3) Boulder 64-65 65-66 Total (inches) (in3)

1 7" 17" 24 13xl6x 4 208 H — — ^ 7x 7x 4 196 2 25' 1' 5" 2615" 12xl0x 3 360 I ------4x 5x 3 60 3 33' 33’ I8xl2x 6 1,296 J ------8x 8x 4 256 4 61'4" — 61*4" 8x 8x 5 320 K — ---- 4x 3x 2 24 5 61' 4" -- , 61*4" 20x16x10 3,200 L ------8x 9x 4 288 6 110' 8'2" 118'2" l4x 8x 7 784 M ------4x 6x 4 104 7 134 16'2"150'2" lOx 5x3-5 175 N ------6x 6x 4 144 8 148*4" 8'5" 156'9" l6x 8x 6 768 P ------8x 7x 4 224 9 ___ 51’ 51’ . 13x 7x 8 728 R I6xl0x 8 1,280 10 —— 51’ 51' l4x 6x 5 420 X ------5x 4x 2 40 A 12x 5x 5 300 © ___ 4x 2x 1 8 B — 811 8" 13x 9x 8 936 * —— 3x 3x1.5 13 C 6x 4x 2 48 • • 6x 3x 1 18 D 4x 7x 2 56 • • * 6x 4x 2 48 E 4x 6x 3 72 •f ------2x 2x1.5 6 • ------F —— 4" 6x 4x 6 144 • • • 3x 3x 2 18 G 8x 5x 4 160

No movement, Moved onto line. Total Volume Moved from 1964 to 1965 12,702 in.3

t-* VJ1 cr\ Motion Study 12: This motion study consists of two lines painted across a complex talus in a large couloir on the south side of Arapaho Valley (Plate I and Pigs. 57 and 58). Slope angles at both lines are 36°. See Tables 29 and 30 for distances and volumes of debris movement onto or away from the motion lines.

Line 1 (highest)

Line 2 (lowest).

2. 4 *

Fig. 57.— Relative positions of rock debris that moved onto or away from lines painted across complex talus 12. Table 29. Movement and Volume of Boulders Involved in Motion Study 12, Line 1.

Movement Dimensions Volume Movement Dimensions Volume Boulder 64-65 65-66 Total (inches (in3 ) Boulder 64-65 65-66 Total (inches) (in3) 1 4 12x7x 10 840 D 22x17x25 9,350 2 7 33x10x13 4,290 P — 1.5 7x11x15 1,155 3 8 16x16x10 2,560 G 8x 5x 3 120 4 17'5" 7x7.5x4 210 H 4" 13Xl2x 9 1,404 5 48*9” 13xl7x 9 1,989 I 5" 7x 5x 3 105

6 23'lln 2f 2tf 27*3” llx 8xl6 1,408 » 55’ 55’ 2x 2x 5 20 A 4" 24x21x40 20,160 © 3’ 2x 2x 4 16 B 9x 6x 4 216 U 2' 2' 4’ 7x 4x 3 84

C 41x11x12 5,^12

No Movement. —Moved onto line. Total Volume Moved 1964 to 1966 49,339 in.3 TABLE 30. Movement and Volume of Boulders Involved in Motion Study 12, Line 2.

Movement Dimensions Volume Movement Dimensions Volume Boulder 64-65 65-66 Total (inches) (in3) Boulder 64-65 65-66 Total (inches) (m3) 1 43*4'' ---- 43F4" I4xl2x 5 840 L ---- 17x 7x 6 714 2 90' 2 f 92' 8x 8x 4 256 N 6x 3x 2 3b

3 96' 8" ---- 96 ’ 8r; 15x 8x 5 60 0 0 24' 2 " —„ 24 *2" 4x 4x1.5 18

4 94f 4" ---- 9414,( 23x11x12 3,036 P l4xl2x 8 1,344

5 117’5" ---- 117 *5" 8x 8x 5 320 R ---- 19x10x19 3,610

A 7" llxl6x 8 1,408 T 9xllx 5 495 B 5x 8x 4 160 V 52" 4" 56T! 4x 3x 3 36

C 139’ ---- 139' llxl6x 8 1,408 w ---- 7xl3x 4 364

D 6x 3x 2 36 X 25' 8,: ---- 6x 4x 2 48

G 12xl2x 4 576 Y ---- 6x 8x 6 288

H ------5x 7x 1 35 Z ------10x12x18 2,160

I ---- 8x 7x 3 168 • 39" ---- 39" 3x1.5x1 5 J 4x 5x1.5 30 xP --- 25x16x16 6,400

K — _ _ 10913" 10913" 20xl4x 9 2,520 No movement, Moved onto line. Total Volume Moved from 1964 to 1966 26,911 in.3 6<5T 160

Fig. 58.— Talus along south side of Arapaho Valley. Numbers show positions of motion studies. Couloir to right is position of motion 12, while couloir at left is position of motion study 13-

Motion Study 13: This motion study is based on two lines painted across complex talus on the south side of Arapaho Valley (Plate I and Figs. 58 and 59). Slope angles range from 35° to 37°. See Tables 31 and 32 for distances and volumes of debris movement onto and away from motion lines. 161

Line 1 (highest).

M- 8 5 7 J K O 6

Line 2 (lowest)

2

Fig. 59.— Relative positions of rock debris that moved onto or away from lines painted across complex talus 13- TABLE 31. Movement and Volume of Boulders Involved in Motion Study 13, Line 1.

Movement Dimensions Volume Motion Dimensions Volume Boulder 64-65 65-66 Total (inches) (in3) Boulder 64-65 65-66 Total (inches) (m3) 1 13" 3" 18" 9x 3x 4 108 D 12x 5x 5 300 2 20" 40" 60" lOx 7x 6 420 E • l6x 6x 8 768

3 30 38 68 15xl0x 4 600 F 13x 6x 5 390 4 5 21 26 13x 7x 4 364 G 19x27x10 5,130 5 6 1 7 15xl0x 8 1,200 H 12x 5x 5 300 6 12 2 14 20xl0x 7 1,400 I 15x 6x 9 810

7 4 4 8 8x 7x 4 224 J 6xllx 9 594 8 10 --- 10 9x 6x 3 162 K 9x 7x 4 252

9 32 1 33 3.5x 8x 6 168 M 4" 4" 19x 8x 3 456 10 7 --- 7 lOx 5x3.5 175 0 8 44 52 3x 3x 3 27 11 44 2 46 3-5x 8x 9 252 Q 31x13x10 4,030 A 13xl4x 4 728 R 46 46 8x 5x 4 160

B 8x 8x 5 320 S 18' 5" 18* 5" 15xl4x 9 1,890

C ---- 6xl4x 7 588 X 12 2 14 7x 3x1.5 32 No movement, moved onto line. Total Volume Moved from 1964 to 1966 21,848 in.^ TABLE 32. Movement and Volume of Boulders Involved in Motion Study 13, Line 2.

Movement Dimensions Volume Movement Dimensions Volume Boulder 64-65 65-66 Total (inches) (in3) Boulder1 64-65 65-66 Total (inches) (in3)

1 9'7" ------9*7" 20xl6x 6 1,920 K ------40 40 65xlOx 3 195

2 19’3" ------19’3" llx 7x 6 462 L 6x 6x 5 180

3 4'11" 5" 5'4" l4x 8x 9 1,008 M ------24 24 8x11x2.5 220

4 31" ------31" 9x 6x 3 162 N ------24 24 8x 5x 7 280

5 25" ------25" 9x 5x2.5 112 P ------2 2 7x 7x 9 441

6 22" ------22" 9xl2x 3 324 T ------5 5 6xl2x 7 504

7 18" 5" 23" 9x 4x 6 216 9 13 22 9x 5x 3 135

A ------2 2 24x20x12 5,760 u 38x19x25 18,050

B ------48x72x36 124,416 V ------I8xl0x 7 1,260

E ------52 52 6x 5x 2 60 X 11'4" 6" ll'lO'" 6x 4x 3 72

F 7xllx 4 308 Y ------11 11 6xllx 6 396

H ------51 51 17x 6x 7 714 • ------30 30 5x 2x2.5 25

♦ • 11'9'i — I ------24 24 5x 6x 3 90 • 11*9" 6x 4x 3 72 J 22 3 25 8x 3x 1 24 ■ 11'9" 38' 7" 50 '4" No movement, moved onto line Total Volume Moved 152,222 in.3 164 Other Examples Results obtained from motion studies on Fair and Taylor rock glaciers are two examples of rock glacier move­ ment outside the area of study. Fair rock glacier is due west of Isabelle Valley on the west side of the Continental Divide at 40° 04’ north latitude and 105° 39' west longi­ tude. The Fair rock glacier motion record from 1961 to 1966, obtained from 14 marked boulders on 3 survey lines, shows, an average surface downvalley movement of 48 cm for the 5 year period or 9-6 cm per year. Taylor rock glacier is in Rocky Mountain National Park on the east side of the Continental Divide at 40° 171 north latitude and 105° 42' west longitude. The Taylor rock glacier motion record from 1961 to 1966, obtained from 11 marked boulders on 4 survey lines, shows a downvalley 5 year average surface movement of 37 cm or 7.4 cm per year. The above studies were initiated by S. E. White and aided by the present writer in 1964 and 1966.

Areas and Volumes of Mass Movement Features The areas and volumes presented in this section per­ tain to features of mass movement in Blue Lake, Isabelle, Green Lakes, and Arapaho Valleys and refer only to those features mapped on Plate I. Other talus deposits are too small to be represented, and were not measured. Most of the areas and volumes were calculated from Plate I. A planimeter was used to obtain areas of the 165 features: thicknesses were then estimated in order to deter­ mine the volumes. Slope angles were not considered, thus considerable error must be expected. The exact configura­ tion of the couloir bottoms beneath talus, and the valley floors beneath rock glaciers, talus toes, and protalus lobes were assumed to be uniform. This introduces further error. The couloirs, as outlined in Plate I are not all filled with rock debris; therefore, estimates of area and thickness had to be calculated from Plate I, serial photographs, and field knowledge. Thicknesses of debris vary from couloir to couloir. The volumes shown in Table 33 are not true rock volumes because the factor of porosity, which may be 30 to 40 per cent, was not considered; therefore, the actual volume of debris is much lower. Table 33 shows figures calculated for the areas and volumes of mass movement features in the four major valleys of study. In each valley except Blue Lake, the area of the south valley wall is larger. The volume of debris is greater on the south valley wall of each valley, and, in most cases, the volume of debris on the south valley wall is much greater than the differences in area should permit. This is thought to be due to protection of the south wall from direct sunlight which allows snow and ice to remain longer and permits more intense freeze-thaw action to take place later into spring and summer. Snow remains much longer 1 6 6

Table 33. Areas and Volumes of Kass Movement.

Area of Rock Glaciers Possible Rock Glaciers Protalus Lobes Scree Talus Valley Valley Valley , Area Volume Area Volume Am folie Area VoIpT Irea Voile Name Side Side (ftj) (ftJ) (ftj) (ftJ) (ftJ) (ft?) ( f t 3 ) (ft2 ) (ft?) (ft2) (ft3)

Blue North 15,170,000 ...... — . 2,390,000 19,020,000 1,230,000 6,570,000 Lake Valley South 10,190,000 ...... 1,060,000 57,^50,000 280,000 890,000 835,000 8,150,000

Isabelle North 9,110,000 ...... —- Valley South 15,900,000 ......

Green North 12,520,000 ...... — Lsikes Valley South 13,970,000 ...... 530,000 3,700,000

Arapaho North 15,870,000 ...... 300,000 6,000,000 Valley South 16,090,000 1,160,000 95,110,000 ....

Totals 1,160,000 95,110,000 830,000 19,700,000 167 Into the summer in couloirs on the south walls. An attempt was made to calculate the time necessary for the deposition of each talus deposit, but It was found there was too much variation. This attempt was made by calculating, from the motion studies, the volume of surface debris movement in a couloir and then dividing this into the estimated volume of the deposit. In some places, two couloirs of the same size and having similar volumes of talus were found to differ as much as 50,000 years for the duration of their deposition. There are a number of reasons why un­ realistic figures were obtained. One and two year records of movement are not necessarily representative of a true aver­ age. A much longer record is needed in order to obtain a true average of debris movement on the talus features. Only the movement of surface debris was recorded. Movement of fines and other debris beneath the talus surfaces was not calculated. Not all movement across the lines could be recorded, rather only that material which moved away from or onto the painted lines could be detected. Porosities and thicknesses of the talus deposits could not be obtained with accuracy. Further error was introduced by assuming that movement across a painted line on a talus deposit was uni­ form for movement on the entire deposit. Because of the above, an accurate estimate for the volume of debris moved was not obtained; therefore, the figures which follow are only approximations. 168 An overall estimate of volume and movement of debris was determined. It was calculated that, on the talus features (complex talus cones and rockfall talus) included In the motion studies, 600 cubic feet of debris moves downward on the valley walls each year. This figure must be taken as representing a minimum amount of movement. The true volume of movement may be twice this amount, therefore, the figures that follow are maxima. This volume of material was moved on talus deposits having an estimated total volume of 10.945.000 ft3. The estimated total volume of talus in the four main valleys is 66,688,000 ft3 (column 5, Table 33)* In proportion, if 600 ft3 moved on talus having a volume of 10.945.000 ft3, then 3056 ft3 should have moved on the remaining 55,743,00 ft3 (66,688,000 ft3-10,945,000 ft3). Dividing the calculated movement of 3656 ft3/year (600 ft3 + 3056 ft3) into the total volume of talus debris (66,688,000 ft3), it Is possible for the volume of talus to have been deposited in 18,475 years. However, two important factors are not considered here. (1) Much of the total volume the mass movement features is actually pore space. The porosity may be 40 per cent or higher in some deposits. If the porosity is 30 per cent, the time for accumulation would be 12,930 years whereas a 40 per cent porosity allows 11,085 years for talus deposition. (2) The above figures are based on the present rate of debris movement, which is not likely to be the same rate for past movement. It is 169 probable that the last few thousand years witnessed periods of Intensive , periods In which the rates of movement and accumulation of debris were many times that for the present. Also there were probably equally long periods of little or no mass movement. Therefore, the figures of 18,475, 12,930, and 11,085 years may be reduced to only fractions of their present values. The above calculations do not take into consideration the large amounts of debris contained in the rock glaciers, possible rock glaciers, and protalus lobes which occupy positions on the valley floors beneath talus on the valley walls. The combined volume of these features plus that of talus is 288,148,000 ft^. Using the present rate of movement, 71,131 years (288,148,000 ft^ 3826 ft^) are necessary to account for the accumulation of this volume of debris. Thirty and 40 per cent porosities reduce this figure to 49,790 years and 42,678 years respectively. Pinedale glaciers are estimated to have been present in the valleys as recently as 7,000 years ago (Richmond, 1965, p. 227). This being the case, the time calculated for the duration of deposition of the mass movement features is much too long; therefore the volume and rate of the present amount of move­ ment of debris are either incorrect or the rate of accumula­ tion was not notably different in the past. In Arapaho Valley, talus deposits behind Temple Lake moraines (3800 to 2000 years B.P.) are not significantly smaller than deposits 170 downvalley from the moraines. This is probably because Temple Lake ice did not reach to the valley walls, and therefore did not clean away pre-Temple Lake talus. The Arapaho rock glacier, whose volume is approximately *45 3110,000 ft lies up valley from Temple Lake moraines. Prom the above evidence, it seems probable that during the period from the close of the Pinedale 7,000 years ago to the present there have been periods of intensive debris accumu­ lation and movement that do not coincide with that of the present.

Summary With the exception of the motion of the rock glaciers, the movement records are for one and two year periods, be­ lieved at this stage to span too short a time to acquire proper significance of rates of movement and amounts of rock material moving downslope. The motion studies, however, were constructed in such a manner as to permit measurements to be continued. Motion studies were made on only a small portion of the total number of mass movement features. Further, the studies cover only a small surface area on each feature. Therefore, the volumes of movement recorded are not neces­ sarily conducive to interpretation of movement of debris of the region as a whole or even of the whole of the feature from which they were obtained. In the construction of these motion studies, areas were chosen where distinct lines could be painted across 171 talus and where boulders were large enough to be drilled and numbered. This selection resulted In a nearly complete disregard of movement of finer debris, and therefore, the volumes pertain necessarily only to the coarser debris. An equal or greater volume of fine material may have moved down- slope in the same time of record. Another possible source of error is the difficulty of constructing and maintaining the motion studies on talus without disturbing the debris. Movement is usually concentrated on certain sections of talus; for example, debris is removed and deposited by meltwater, mudflows, and avalanches. Movement on protalus lobe and rock glacier fronts is sporadic. Arapaho rock glacier (Pig. 55) appears to have moved as a unit with maxi­ mum forward movement in the central portion. Total volume of recorded movement was 1,700,000 cubic inches or 1,000 cubic feet. Of this total, 1,300,000 cubic Inches was on talus and therefore represents downslope movement of the valley walls. DESCRIPTIONS OP GLACIAL FEATURES AND THEIR RELATION TO MASS MOVEMENT FEATURES

Introduction Very little has been done on glacial features especi­ ally those related to the more recent time known as Neogla­ ciation. Madole (i960 and 1963) described and mapped some of the glacial features in Isabelle, Pawnee, Blue Lake, and Audubon Valleys. Ives (1953b) described glacial features in Arapaho Valley especially near Island, Goose, and Silver Lakes. Thornbury (1928) studied glaciation of the east side of the Colorado Front Range between Longs Peak and James Peak. In each case, Neoglaciation features in the upper portions of the valleys were not described In any detail. Heterogeneity appears to be characteristic of glacial features from valley to valley. Glacier ice during the Neoglaciation appears to have been abundant in some valleys, sparsely present in some, and absent in others. Correlation between valleys Is difficult. At least six glacial stages and stades of Pleistocene glaciation were identified. Substages or stades of Wisconsin glaciation are recognized to the east, but none were dis­ tinguished In the upper valleys. For the most part, Richmond’s (1965, p. 227) classification of glaciation of the

172 173 Rocky Mountains is used (Table 4). (1) The first stage of glaciation, represented here by Niwot Ridge till, following Madole (I960, p. 26), occurred presumably prior to erosion of the present deep valleys. This glaciation is almost certainly pre-Bull Lake (pre-Wisconsin) and is thought to result from an ice cap that was not confined to valleys but spread out as a sheet over the higher parts of the range. (2) Bull Lake (early Wisconsin) till has questionable exis­ tence in the upper valleys of this area. At two locations, till contains boulders with deeply pitted and weathered sur­ faces. These tills are thought to be Bull Lake, based on the degree of weathering. (3) Pinedale glaciation (late Wiscon­ sin) is characterized as thin discontinuous sheet-like deposits of till on valley floors or as segmented lateral moraines in the lower parts of valleys. (4) Temple Lake stade (early Neoglaciation) is represented by well developed, although small, moraines, especially in Arapaho Valley. According to Richmond (1965, p. 227), the Temple Lake stade spans the period of time from 4000 to 900 B.P. (5) Benedict (1966, personal communication) has given the stade name Arikaree to the late part of Richmond's Temple Lake stade because it is evident that an intermediate advance occurred approximately 1600-1000 years ago (Benedict, 1966, p. 29). The Arikaree stade should be thought of as an intermediate stade between and of equal rank to the Temple Lake and Gannett Peak stades. (6) Gannett Peak stade (late 174 Neoglaciation) is represented by recent or m o d e m moraines around the fronts of the present little glaciers.

Intervalley Glaciation Niwot Ridge till represents the oldest recognized glacial deposit in the area. It Is believed to have resulted from pre-Wisconsin ice-cap glaciers that occupied the summit regions of the Front Range prior to the time of valley cut­ ting. It appears evident that the ice-cap glaciers expanded from the summit areas onto a previously formed undulating erosion surface now severely dissected and formerly recog­ nized as the Flattop peneplain. Resulting glacial deposits were sheet-like tills deposited on the old erosion surface and now remain on the upland interstream areas. Remnants of the old surface are shown In Figure 60. Blackwelder (1915) defined the "Buffalo glacial stage" from similar pre- Wisconsin Interstream till deposits in the Wind River and Teton Mountains of Wyoming. Richmond (1957, 1962, and 1964) found three superposed pre-Bull Lake tills, separated by interglacial soils, in Glacier National Park, Wind River Mountains, and the La Sal Mountains. He suggests the three tills may represent Nebraskan, Kansan, and Illinoian glaci­ ations. These three tills are not yet recognized here in this part of Colorado. As Indicated above, Niwot Ridge till occupies those portions of the old erosion surface that are now present as Interstream divides. The tills believed to be of this age 175 are shown on Plate I, Figure 60, and listed below. Four major deposits of Niwot Ridge till were recognized: (1) on the old erosion surface between Mount Albion and Kiowa Peak, (2) on a large portion of Niwot Ridge, (3) on the ridge between Lake Isabelle and Blue Lake Valley, and (4) on the southwest Flank of Mount Audubon. These deposits lie approximately between 11,300 and 12,400 feet. Moraines are not distinguishable on the Niwot Ridge till, which has a surface of little relief except for a few post-glaciation solifluction lobes that reach 15 feet in height. The till appears to conform to the general slope and configuration of the old erosion surface. It is com­ posed of unsorted debris with boulders of 3 to 5 feet being common. In general the boulders were subrounded but angular frost-shattered boulders now are common. Patterned-ground features occur on all of the Niwot Ridge till deposits with the following types being present: sorted polygons, sorted stripes, nonsorted circles, nonsorted nets, sorted lobes, sorted terraces, nonsorted lobes (solifluction lobes), and nonsorted terraces (solifluction terraces) (Benedict, 1965, p. 23). In some places an individual net may reach 15 feet in diameter. Solifluction lobes are quite common on the gentle slopes. In most places the till grades Into scree slopes on the valley sides making it difficult to place an accurate boundary. Fig. 60.— View to the west perpendicular to the north-south trend of the Colorado Front Range. A * Mount Audubon, N * Niwot Ridge, B * Blue Lake Valley, I * Isabelle Valley, G = Green Lakes Valley, Ap = Arapaho Valley, K = Kiowa Peak, Ma * Mount Albion, and t ■ surfaces covered by Niwot Ridge till. Note the undulating nature of the old erosion surface. 177 According to Madole (I960, p. 28), the soil on the Niwot Ridge till is shallow and poorly developed for its supposed pre-Wisconsin age. However, he attributed this to low temperatures at the high altitude and the Inability of the till to retain moisture, both of which retard chemical weathering and subsequent formation of soil. Till on Niwot Ridge overlies the Audubon-Albion monzonite stock of early Eocene or possibly Paleocene age, yet much of the till contains large boulders of Precambrian granite and gneiss (Wahlstrom, 19^7, p. 562). According to Madole (I960, p. 28), Idaho Springs schist comprises 30 per cent of the till, and Silver Plume granite and monzonite from the underlying stock contribute M per cent. This being the case, glaciation seems necessary to account for schist and granite being on top of the monzonite stock.

North Fork Middle Boulder Creek Valley North Pork Middle Boulder Creek Valley is the southern­ most valley included in this investigation. Very little field time was devoted to this valley. Glacial and mass move­ ment features were mapped but no motion studies were made here. Tills of Bull Lake age or older were not identified in that portion of North Fork Middle Boulder Creek included on Plate I. Pinedale glaciation is represented by a moraine that forms Lake Dorothy, segments of lateral moraine along 178 the north and south sides of the valley, and scattered boulders and patches of till on the valley bottom. Moraines, thought to be Temple Lake, form two lakes in the south cirque of this double-cirqued valley. The degree of weather­ ing on surface boulders of this moraine appears to be less than on the moraine at Lake Dorothy. The Gannett Peak stade is represented by a small moraine high on the valley wall south of Lake Dorothy. This moraine is composed of fresh debris. Protalus lobes are numerous along the south valley wall and are superposed on a Pinedale lateral moraine. These lobes can be dated only as post-Pinedale. One protalus lobe is behind the moraines mapped as Temple Lake, and therefore, it is thought to be post-Temple Lake.

Arapaho Valley Bull Lake till was not identified in the upper part cf Arapaho Valley by the present investigator. Ives (1953, p. 240) mapped Bull Lake till as occurring on the valley wall north of Goose and Island Lakes (Plate I). The evidence of Pinedale glaciation is scattered till patches and glacial boulders on the valley floor. A patchy lateral moraine occurs along the north edges of Goose and Island Lakes and adjacent to Bull Lake till. Early Neoglaciation is represented by Temple Lake moraines approximately two-thirds of a mile downvalley from the Arapaho glacier. Richmond (I960, p. 1381) estimates the 179 Temple Lake stade to have formed from about 3800 to about 2000 years ago. The Temple Lake moraines form well- developed loops on the valley floor. Segmented lateral moraines occur along the valley walls. Medial-like moraines are in the center of the valley, but they are actually coalescing lateral moraines that formed between two ice lobes (Plate I). The downvalley terminal moraine is approx­ imately 60 feet high at its distal edge whereas its upvalley side is nowhere more than 20 feet above the ground moraine behind the end moraine. Two loop moraines and a coalescing lateral moraine occur approximately 800 feet upvalley from the terminal moraine and probably represent recessional moraines formed as the ice retreated and divided into two tongues. The loop on the north side of the valley, behind which a lake formed, represents deposition by a distinct ice tongue that occupied the deeper part of the valley. The smaller loop moraine on the south side of the valley was deposited by a smaller narrower ice tongue on that side of the valley. Division into two ice tongues is believed to have been caused by the large bedrock outcrop that projects into the valley from the south side and caused the ice to be much thicker on the north side of the valley. It Is be­ lieved that Temple Lake ice advanced to the position of the terminal moraine where deposition took place. As the glacier retreated, downwasting took place; the lower end of the glacier was divided into two lobes; and the coalescing 180 lateral moraines between the two lobes were deposited. Either a stabilization or an advance of the Ice resulted In the deposition of the two upvalley loops. The northern ice tongue, being much thicker, deposited a distinct moraine, 30 to 35 feet high, behind which is a lake. The ice tongue occupying the south side of the valley being much thinner, because of the bedrock projection beneath, deposited a well developed but a much smaller loop moraine. The next recorded glaciation in the Front Range and Rocky Mountain region is Gannett Peak stade, which is repre­ sented by moraines at the front of present glaciers. Accord­ ing to Bennecit (1966, p. 29), the Gannett Peak glaciation began 3 to 4 centuries ago and may still be in progress. However, in Arapaho Valley, dates of 1000 + 90 B.P. years obtained from glacial ice beneath the Arapaho rock glacier suggests an intermediate stade between Temple Lake (3800-2000 years B.P.) and Gannett Peak (400 years B.P.- present). Also weathering of the boulders and lichen dif­ ferences on the rock glacier surface suggest that it is considerably older than the material composing the Gannett Peak moraine. Benedict (1966, personal communication) has designated the name Arikaree for this kitermediate stade. His reasoning is further evidenced by radiocarbon dates, obtained from stone banked terraces on Niwot Ridge where sollfluction lobes formed 3000 to 2500 years ago during late Temple Lake time, which showed a period of rapid downslope 181 movement during the period from 1000 to 1250 years B.P. (Benedit, 1966, p. 29). The solifluction lobes buried 14 organic layers now dated by the C method. As indicated above, late Neoglaciation is represented by the Gannett Peak moraine around the front of Arapaho glacier (Plate I). The moraine is composed of fresh boulders, has no soil, and supports no vegetation except sparse lichen and scattered pioneer plants. The moraine is double and possibly triple crested, suggesting small readvances and pauses during ice retreat. Photos of Arapaho glacier in 1898 (Waldrop, 1964) show that the glacier at that time was in contact with the inner moraine. Waldrop (1964, p. 1) states the glacier has receded 300 to 900 feet across its front since its last maximum around i860, and since that time has lost 32 per cent of its surface area. Placing all features of mass movement into a particu­ lar period of time is rather difficult. Those features down­ valley from the Temple Lake terminal moraine can only be dated as post-Pinedale because Pinedale ice is known to have filled the valley. The protalus lobe complex north of Goose Lake is definitely post-Pinedale and probably pre-Gannett Peak based on tree ring dates of 550 years obtained from trees growing on the complex. Most mass movement features appear to be at least post-early-Temple Lake to the present. The distal portion of an avalanche boulder tongue rests on the north edge of the Temple Lake terminal moraine (Plate I). Complex talus cone No. 12 is behind an upvalley loop moraine. Complex talus cone No. 11 and numerous other smaller talus cones are superimposed on the Temple Lake lateral moraine. Formation of present mass movement features upvalley from the Temple Lake terminal moraine is thought to have begun immediately after maximum Temple Lake time and continued to the present. Maximum activity probably occurred during Arikaree and Gannett Peak times, both of which would have produced periglacial conditions necessary for maximum accumulation of mass movement features.

Henderson Valley Henderson Valley is a hanging valley that hangs 700 to 800 feet above the floor of Arapaho Valley. The valley floor is till-covered, but the exact age of this till is still in doubt. Based on the following evidence, the till is thought to be old: (1) Moraines occur, but they are dis­ sected and vaguely formed. (2) Surface boulders are deeply pitted due to chemical weathering and wind blasting of the less resistant minerals (Fig. 61). Both processes involve considerable time, especially chemical weathering at this altitude of approximately 12,000 to 12,400 feet. (3) Pat­ terned ground, especially sorted polygons, is common on most of the till. (4) Most boulders are subrounded but angular rock fragments produced by extensive frost shattering are common. These features, none of which are common on Temple Lake or Pinedale tills in the area, require considerable 183

Pig. 61.— Pitted surface of boulders on the floor of Henderson Valley. See knife for scale. time for their formation. It is realized that they are developed at an altitude higher than comparable features in nearby valleys but it is believed that this difference in altitude Is not sufficient to produce the differences of character. Based on the above evidence, it is suggested that the tills occupying the floor of Henderson Valley are either Bull Lake or possibly Pinedale in age. It seems quite pos­ sible that Pinedale ice did not occupy this valley except possibly in the upper cirque next to the present head wall. The possible rock glacier on the north side of the valley, resting on the older till, could be Temple Lake or Arikaree in age. Till at the front of Henderson glacier appears to be younger than the older till described above. Its surface Is covered by poorly developed sorted polygons, 184 but the boulders show little effects of weathering. This till is probably Temple Lake or possibly Arikaree. A small, double-crested moraine is present at the southeast edge of Henderson glacier. This moraine is composed of fresh debris and is considered a Gannett Peak moraine.

Neve Valley Neve Valley is a hanging valley with a cirque floor at approximately 11,200 feet. Glacial features are not abundant. This valley lacks evidence of Bull Lake till or Pinedale till; however, the valley was surely cut during Pinedale and has been occupied most of the time since then. Segmented moraines occur near the mouth of the valley and adjacent to the bedrock riegel. These moraines are believed to be Temple Lake in age and correlative to the loop moraines in Arapaho Valley (Plate I). A small Gannet Peak moraine is in front of a snowbank or small glacier on the steep slope below the col between Henderson and Ne've' Valleys. Between the moraine and the valley floor are two small lobes of debris that resemble protalus lobes, but are believed to be morainal and talus debris that has moved downslope per­ haps during the Arikaree stage.

Green Lakes Valley Bull Lake till was not identified on the upper part of Green Lakes Valley by the investigator, but Ives (1953, p. 240) mapped till of this age south of Lake Albion (Plate I). 185 This till is on the south side of the valley and above the Pinedale lateral moraine. Pinedale till is represented by isolated boulders and patches of till, some of which resemble moraines. Both Lake Albion and Green Lake No. 1 have moraine-like patches of till along their downvalley sides although the moraines do not appear to be responsible for the origin of the lakes. Pinedale lateral moraines occur on the both sides of the valley at the eastern margin of the area of investigation. The effects of Temple Lake ice in this valley are not identified for certain. The possible rock glacier in Arikaree cirque is superimposed on a moraine of either late Pinedale or early Temple Lake age. Between the possible rock glacier and Arikaree glacier is a triple crested moraine (Pig. 8). The position of this morainal complex is comparable to those of Gannett Peak, but boulders on the outer two crests show a lichen growth similar to that on the Arapaho rock glacier, thus suggesting a minimum age of Arikaree or possibly late Temple Lake (Laughlin, 1966, personal communication). The inner moraine crest, which is lowest, does not have a dis­ tinct lichen cover and it is therefore suggested that this portion of the moraine is probably of Gannett Peak age. The exact age of the possible rock glacier is uncertain because the age of the till on which it rests is not identified. The probable age is post-late Pinedale or post-early Temple Lake continuing to the present. It is probable that the possible 186 rock glacier was forming during the formation of the Arikaree or late Temple Lake triple-crested moraine complex. Mass movement features, mainly proscree lobes and talus in the cirque, sire post-early Temple Lake because ice is thought to have occupied the cirque at that time. Those features of mass movement downvalley from the cirque can only be dated as post-Pinedale. The protalus and proscree lobes, however, are believed to have had their maximum move­ ment and lobe formation during periods of glacial activity following the Pinedale. If this is the case, lobe formation and movement most likely had maximum occurrence during all Temple Lake, Arikaree, and Gannett Peak stades, but with less activity since Gannett Peak time. Complex talus cones and rockfall talus, mudflows, avalanche boulder tongues, and protalus ramparts, all of which occur throughout this valley, may have also witnessed maximum activity during post-Pinedale glacial stades.

Isabelle Valley Bull Lake till was not identified in the upper part of Isabelle Valley. Pinedale till upvalley from Lake Isabelle is characterized by isolated boulders and patchy till deposits. Downvalley from Lake Isabelle, Pinedale till occurs as ground moraine on the valley floor and as a weak segmented lateral moraine along the north side of the valley (Plate I). 187 Two closely spaced Temple Lake moraines are in the south cirque at the head of Isabelle Valley and are thought to be correlative with the loop moraines of Arapaho Valley. Evidence of glaciation comparable to the Arikaree stage was not observed. Late Neoglaciation is represented by a triple­ crested Gannett Peak moraine lying near the front of Isabelle glacier and perched on the bedrock riegel. The triple­ crested nature of the moraine corresponds to the Gannett Peak moraine in Arapaho Valley and represents small read­ vances or pauses during general ice retreat. The moraine is composed of fresh boulders, has no soil, and supports no vegetation except sparse lichen and scattered pioneer plants. Most mass movement forms can be broadly termed as post-Pinedale because they occur in a valley formerly occu­ pied by Pinedale ice. Features, here, like those of other valleys, are thought to have started development shortly after Pinedale time and continued to the present with periods of acceleration and movement corresponding to Temple Lake, Arikaree, and Gannett Peak stades of glaciation. The avalanche boulder tongue in the south cirque is post-Temple Lake because its distal part rests on Temple Lake till. Downvalley from the cirque, protalus lobes and talus cones rest on the valley floor that was last glaciated by Pine­ dale ice. The large protalus lobe complex on the south valley wall is probably the accumulative result of debris accumulation and movement during all of Neoglaciation. 188 Pawnee Valley Pinedale till Is the oldest glacial deposit In Pawnee Valley. It occurs as Isolated boulders and sporadic ground moraine over most of the valley floor; but near the mouth of Pawnee Valley, near the junction with Isabelle Valley, a small but distinct moraine exists (Plate I). This moraine is below tlmberline and has a maximum height of approxi­ mately 25 feet. It is believed to be late Pinedale (Pinedale III stade, after Richmond, 1965) and resulted when the ice in Isabelle Valley retreated up the main valley beyond the junction of the two valleys. The moraine may represent an advance of ice in Pawnee Valley. A corresponding moraine was not identified in Isabelle Valley. Temple Lake stade is represented by two cirque mor­ aines. The peculiarity of these two moraines is that they are oriented in such a manner that they could not have been deposited by the same glacier (Plate I). Two small glaciers apparently existed during Temple Lake time, one on the west side of the cirque and one at its head, west of and adjacent to the bilobate protalus lobe. This resulted in the deposition of a south-facing moraine and an east-facing moraine. It is not possible to determine whether or not the two small glaciers existed simultaneously. Ages of mass movement features In this cirque appear to be mostly post-Temple Lake based on the assumption that the two moraines are of Temple Lake age. A protalus lobe has 189 developed on the valley wall behind the Temple Lake moraine on the west side of the valley, and an avalanche boulder tongue Is superimposed on the moraine at the head of the valley, indicating that both features are post-Temple Lake. A larger bilobate protalus lobe is now near the cirque head- wall east of the two moraines (Pig. *17). This protalus lobe may also be post-Temple Lake, but no evidence exists that indicates it could not have been at least partially developed while the moraines were being formed. It is not superimposed upon nor is it in turn covered by Temple Lake debris; there­ fore, it can only be dated as post-Pinedale. Evidence for Arikaree or Gannett Peak glaciation was not discovered although activity of the mass movement features was probably increased during these two stades.

Blue Lake Valley Till of Pinedale age is the oldest glacial deposits recognized in Blue Lake Valley. Upvalley from Mitchell Lake, Pinedale deposits are represented by Isolated boulders and sporadic accumulations of till. Numerous bedrock steps are on the valley floor and it is around these steps that patches of till have lodged and accumulated. Along the base of the south valley wall, a segmented lateral moraine occurs. Numerous patches of till give the vague impression of a series of recessional moraines between Mitchell and Shallow Lakes, but close inspection reveals that these till patches 190 correspond In position to the bedrock steps on the valley floor. Shallow Lake is dammed by what appears to be a loop moraine believed to be late Pinedale. Distinct Pinedale end moraines are downvalley from Mitchell Lake, one of which is responsible for the formation of the lake. This moraine is believed to be late Pinedale (Pinedale III, personal agree­ ment in field by S. E. White and G. M. Richmond, 1965). Numerous Temple Lake moraines are in both cirques. They are rather short, oriented at various angles, and soil covered (Plate I). It appears as if at least three sub­ stages occurred during Temple Lake time In order to account for the three moraines in the south cirque. This corres­ ponds closely to Temple Lake moraines in Arapaho Valley. The great complex of protalus lobes on the south side of the valley may be comparable to Arikaree stade of glaciation. Gannett Peak stade is represented by a small recent moraine in the north cirque. Mass movement features can be dated only with respect to their positions relative to glacial deposits. The ara- lanche boulder tongue In the south cirque is post-late Temple Lake because it is superimposed onto the Inner Temple Lake moraine. Figure 16 shows the vast complex of protalus lobes along the south side of the valley. South of Shallow Lake (Fig. 16 and Plate I) and at the base of the valley wall, protalus lobes have built out onto the top of what is believed to be a late Pinedale lateral moraine, thus 191 Indicating that the protalus lobes are at least post-late Pinedale. Again, maximum movement and accumulation constitut­ ing the mass movement forms are believed to have taken place during post-Pinedale glacial stages. It must be noted that a considerable period of time is necessary for accumulation of debris after the Pinedale ice disappeared.

Audubon Valley Audubon Valley is a small hanging tributary valley north of Mitchell Lake In Blue Lake Valley. Its floor slopes from 11,200 feet at its mouth to 11,700 feet at its head. Distinctions between glacial tills are made solely on the basis of the degree of weathering of surface boulders. This suggests that tills of three glacial stages are present here. The oldest till is thought to be late Bull Lake and Is characterized by weathered monzonite boulders on which the feldspar phenocrysts, being more resistant than the groundmass minerals, project 1 to 1 1/2 Inches on boulder surfaces. Monzonite boulders Included in Pinedale till in Blue Lake Valley do not show this weathering phenomenon and for this reason this older till Is considered to be at least late Bull Lake. This till is on the south side and at the mouth of the valley. If this is Bull Lake, Its location makes improbable that post-Bull Lake Ice ever extended out of the valley. A questionable Pinedale till is believed to butt against the Bull Lake till and to be approximately two- thirds of the way down the valley (Plate I). Weathering of 192 boulders on this till is of a lesser degree. However, the question exists as to whether this till could not also be late Bull Lake and to this question the writer has no definite answer. Till indicated as Temple Lake on Plate I in this valley is composed of boulders that show little or no effects of weathering. Feldspar crystals do not project significantly above any of the boulder surfaces. The avalanche boulder tongues and protalus rampart are superimposed onto Temple Lake moraines and are there­ fore post-Temple Lake in age. The protalus lobe is not superimposed on any material that can be given a definite age, but its boulders show the same degree of weathering as those on the Temple Lake moraines; it is thus possible that this lobe formed during Temple Lake time.

Summary and Conclusions Pre-Wisconsin glaciation, represented here by Niwot Ridge till, occurs on intervalley divides (Fig. 60). Freez­ ing and thawing has altered the original character of this old till and has made it difficult to place it within a definite time interval. Evidence of Bull Lake glaciation, within the upper parts of the valleys studied here, is based on the degree of weathering on surface boulders. Surface boulders showing a high degree of weathering and thought to be Bull Lake age are in Henderson and Audubon Valleys. Moraines of this stage are poorly developed. 193 From the previous discussions and descriptions, it is rather obvious that a distinct lack of recessional moraines for Pinedale glaciation exists within the valleys. Evidence of two and three advances occurs east of the area of study. Lack of recessional moraines and the occurrence of sporadic accumulations of till and isolated boulders suggest that Pinedale ice shrank more by surface melting than by frontal retreat. Pinedale glaciation appears to have been consis­ tent, with distinct moraines occurring in the lower portions of valleys to the east, but with sporadic accumulations of till in the upper parts of the valleys. Pinedale ice appears to have filled all major east-west valleys. The Temple Lake stade is represented differently in each valley. Distinct loop moraines occur three-quarters of a mile downvalley from the Arapaho glacier in Arapaho Valley. In the other valleys, Temple Lake moraines indicate that ice during that time did not extend downvalley beyond the immedi­ ate cirque area. Temple Lake moraines are well-developed only in Arapaho Valley. With the exception of Arapaho Valley, ice during the Temple Lake stade was not extensive enough to be called valley glaciers. Arikaree glaciation, a term introduced by Benedict (1966, personal communication), may be important in relation to mass movement features. Organic material in glacier ice beneath the Arapaho rock glacier and in plant material beneath solifluction lobes on Niwot Ridge yield dates of 1 9 H 1000 to 1250 years B.P. It Is this Interval of time that Benedict has called Arikaree. If the accumulation and move­ ment of debris forming the Arapaho rock glacier is attributed mainly to Arikaree time, then it is logical that many of the forms of mass movement may also be the same age. The protalus lobe complexes in Blue Lake and Isabelle Valleys may have had the greatest amount of accumulation and movement during the Arikaree stade. Gannett Peak glaciation Is represented by modem moraines at the fronts of Arapaho, Henderson, Arikaree, and Isabelle Glaciers. Mass movement features are dated as being post-(glacial age). Many are dated as post-Bull Lake or post-Pinedale, but it should be noted that long periods of time are necessary for accumulation of debris that constitutes the mass move­ ment forms; therefore, it Is unlikely that they developed to their present form soon after ice retreat. Mass movement features similar to those in the valleys today may have formed after Bull Lake glaciation, but were destroyed and Incorporated into Pinedale till. Debris probably began to accumulate soon after the disappearance of a particular glacier, and If not destroyed by later glaciation, its accumulation and movement were surely accelerated. A notable feature is the location of protalus lobes. None are superimposed on Temple Lake material. They occur beside or in front of but never on material of this stade. Only one small lobe occurs behind a Temple Lake moraine but it is positioned such that it might have formed at the same time as the moraine. It is the writer’s opinion, based on evidence stated here and in the preceding paragraphs, that greatest periods of accumulation and movement of debris was during Temple Lake and Arikaree stades with possibly the greatest movement of debris during the Arikaree stade. REFERENCES CITED

Andersson, J. G. , 1906, Solifluction, a Component of Sub­ aerial Denudation: Jou. of Geol., vol. 14, p. 91-113* Atwood, W. W., and Atwood, W. W. Jr., 1938, Working Hypoth­ esis for the Physiographic History of the Rocky Mountain Region: Geol. Soc. Amer. Bull., vol. 49, p. 957-980. Behre, C. H., 1933, Talus Behavior above Timber in the Rocky Mountains: Jour. Geol., vol. 4l, p. 622-635. Benedict, James B., 1966, Radiocarbon Dates from a Stone- Banked Terrace in the Colorado Rocky Mountains, U.S.A.: Geografiska Analer, vol. 48. Series A, p. 2 4-31. Blackwelder, Eliot, 1915, Post Cretaceous History of the Mountains of Southwestern Wyoming: Jour. Geol., vol. 23, p. 97-117, 193-217, 307-340. Brown, W. H., 1925, A Probable Fossil Glacier: Jour. Geol., vol. 33, No. 4, p. 464-466. Bryan, Kirk, 1934, Geomorphic Processes at High Altitudes: Geog. Rev., vol. 24, p. 655-656. Capps, S. R., 1910, Rock Glaciers in Alaska: Jour. Geol., vol. 18, p. 359-375. Chaix, Andre, 1923, Les de blocs du Pare National Suisse d'Engadine (note preliminaire): Le Globe (Organe de la Societe de Geographie de Geographic de Geneve, v. 62, p. 1-34. Cross, Whitman, and Howe, Ernst, 1905, Geography and General Geology of the Quadrangle in Silverton Falio: U.S. Geol. Survey Geologic Folio no. 120, Silverton Folio, p. 1-25. Davis, W. M., 1911, The Colorado Front Range: Assoc. Amer. Geog. Ann., vol. 1, p. 21-84.

196 197 Poster, H. L., and Holmes, G. W., 1965, A Large Transitional Rock Glacier in the Johnson River Area, Alaska Range: in Geological Survey research 1965; U.S. Geol. Survey Prof. Paper, no. 525-B, p. B112-B116. Howe, Ernest, 1909, Landslides in the San Juan Mountains Colorado: U.S. Geol. Survey Prof. Paper, no. 67, 58 p. Ives, Ronald L., 1940, Rock Glaciers in the Co^ado Front Range: Geol. Soc. Amer. Bull., vol. 51, p. 1271-1294. Ives, R. L., 1953a, Anomalous Glacial Deposits in the Colorado Front Range Area, Colorado: Trans. Amer. Geophs. Union, vol. 34, no. 2, p. 220-226. Ives, R. L., 1953b, Later Pleistocene Glaciation in the Silver Lake Valley, Colorado: Geog. Rev., vol. 63, p. 229-252. Kesseli, J. E., 1941, Rock Streams in the Sierra Nevada, California: Geog. Rev., vol. 31, P. 203-227. King, P. B., 1959, The Evolution of : Prince­ ton University Press, 190 p. Knight, S. H., 1964, The Geologic Background of the Boulder Area; in Natural History of the Boulder Area: Univer­ sity of Colorado Museum, leaflet no. 13, p. 1-9. Lahee, Frederic H., 1931, Field Geology, 3d ed,, McGraw-Hill Book Co., Inc., 789 p. Lee, W. T., 1923, Peneplains in the Front Range and Rocky Mountain National Park, Colorado: U.S. Geol. Survey Bull., 730 A., p. 1-19. Leopold, Luna B., Wolraan, Gordon M., and Miller, John P., 1964, Fluvial Processes in : W. H. Freeman and Company, 522 p. Lovering, T. S., and Goddard, E. N., 1950, Geology and Ore Deposits of the Front Range, Colorado: U.S. Geol. Survey Prof. Paper, no. 223, 319 p. Madole, R. F., I960, Glacial Geology of Upper South St. Vrain Valley, Boulder County, Colorado: Unpublished Master's thesis, The Ohio State University, 109 p. Madole, R. F., 1963, Quaternary Geology of St. Vrain Drainage Basin, Boulder County, Colorado: Unpublished Ph.D. dissertation, The Ohio State University, 289 p. 198 Marr, J. W. , 1961, Ecosystems of the East Slope of the Front Range In Colorado: University of Colorado Studies, Series in Biology No. 8, Univ. Colo. Press, Boulder, Colorado, 134 p. Osburn, William S.; Benedict, James B.; and Corte, Arturo E. , 1965, Frost Phenomena, Patterned Ground, and Ecology on Niwot Ridge: INQUA, International Assoc, for Quatern­ ary Research Vlith Congress, Guidebook for One-Day Field Conferences, Boulder Area, Colorado, p. 21-27. Outcalt, Samuel I., and Benedict, James B., 1965, Photo- Interpretation of Two Types of Rock Glaciers in the Colorado Front Range, U.S.A.: Jour, of Glaciology, vol. 5, no. 42, p. 849-856. Outcalt, Samuel I., and MacPhail, Donald D., 1965, A Survey of Neoglaciation in the Front Range of Colorado: Uni­ versity of Colorado Studies, Series in Earth Sciences, no. 4, 124 p. Paddock, Mark W., 1964, The Climate and Topography of the Boulder Region; in Natural History of the Boulder Area: University of Colorado Museum, leaflet no. 13, p. 25-34. Rapp, Anders, 1959, Avalanche Boulder Tongues, Lappland, Descriptions of Little-Known Forms of Periglacial Debris Accumulations: Geografiska Annaler, H&fte I, p. 34-48. Rapp, Anders, i960, Recent Development of Mountain Slopes in K&rkevagge and Surrounding Northern Scandinavia: Geografiska Annaler, vol. 42, nos. 2-3, p. 73-200. Rapp, Anders and Rudberg, Sten, i960, Recent Periglacial Phenomena in Sweden: Bull. Periglacjalny, no. 8, p. 143-154. Richmond, G. M., 1948, Modification of Blackv^Lder's Sequence of Pleistocene Glaciation in the Wind River Mountains: Geol. Soc. Amer. Bull., vol. 59, P* 1400-1401. Richmond, G. M., 1952, Comparison of Rock Glaciers and Black Streams in the La Sal Mountains, Utah (Abstract): Geol. Soc. Amer. Bull., vol. 63, p. 1292-1293. Richmond, G. M., 1957, Three pre-Wisconsin Glacial Stages in the Rocky Mountain Region: Geol. Soc. Amer. Bull., vol. 68, p. 239-262. Richmond, G. 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Plate I. Map of Mass Movement and Glacial Features of the upper Drainage Areas of South St. Vrain Creek, North Boulder Creek, and North Fork Middle Boulder Creek, Boulder County, Colorado. ss

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EXPLANATION

G a n n e tt Peak Till PRG-*Possibie-Rock G lacier ?.•>: \ " Ne°- glaciation Temple Lake Till PR -+Protalus Rampart

Late Pjnedale Till RF -iRockfall Talus W isconsin A8T~>Avalanche Boulder Tongue Early ( Boll Lake Till Wisconsin LM-iLateral Moraine v \ Pre- f PG-*Pattemed Ground W isconsin Niwo1 RidS e Til1

^— w / Profalus Lobe Ji, Undifferentiated Talus Cones

fs 1 Scree ? Questionable Age

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Lighter shades indicate ground moraine and sporadic till RG Rock Glacier \ $ ^ I \

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Lighter shades indicate ground moraine and sporadic till RG -* Rock Glacier / p 7S h ;

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CONTOUR INTEI DATUM IS MEAI : 12000 \ 1 MILE

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