BULLETIN 94 LAND UsE GEOLOGY of CENTRAL JACKSON COUNTY, OREGON 1977 � cw--o.._ON- ...... o•PARTM-T � ANIJ" .....AL IN..,.R(•• Q .. RA�H MMIDN. -A'Ta s. ·�lb' STATE OF OREGON DEPARTMENT OF GEOLOGY AND MINERAL INDUSTRIES 1069 State Office Building, Portland, Oregon 97201 Bu lletin 94 LAND USE GEOLOGY OF CENTRAL JACKSON COUNTY, OREGON John D. Beaulieu Oregon Department of Geology and Mineral Industries and Paul W. Hughes, Consulting Geologist Conducted in compliance with ORS 516.030 Funded in port with a grant from the Land Conservation and Development Commission to Jackson County GOVERNING BOARD STATE GEOLOGIST Leeanne MacColl Portland Ra I ph S. Mason Robert W. Doty Talent 1977 John L. Schwabe Portland CONTENTS INTRODUCTION 1 Purpose ---------- 1 Acknowledgments - - - 1 How to Use - 1 General - - -· - ----- 1 Site evaluations ---- 2 Land use capability ana lyses - 2 Extrapolation of data 2 Policy formu loti on - - -- 2 Map Scale and Detai I - - --- - 2 GEOGRAPHY ---- 5. Location and Extent - 5 Climate ---- 5 Topography --------- 5 Popu lotion and Land Use ------- 6 GEOLOGIC UNITS 7 Genera I -- - -- 7 Surficial Geologic Units - --- --- 7 Quaternary alluvium ------ 7 Quaternary older alluvium ----- - ---- 7 Quaternary bench grave I -- --- 8 Quaternary alluvial fan deposits - - - -- 10 Volcanic and Sedimentary Geologic Units --- 10 Pliocene basalt - ---- -- - 10 Eocene and Oligocene volcanic rock --- 10 Eocene and 0 ligocene tuffaceous rock - - - - - - - 12 Eocene sedimentary rock - - - ---- 13 Cretaceous sedimentary rock - --- 14 Galice Formation - - -- - - -- - -- 14 Metamorphic Geologic Units - - - - - 14 Volcanic rocks of the Applegate Formation - - - - - - 15 Sedimentary rocks of the Applegate Formation - - --- 15 May Creek Schist ----- ------ 16 Intrusive Geologic Units ---------- 16 Diorite and granodiorite ----------- 16 Gabbro ----- ----- 17 Serpentinite ---- 17 Tertiary intrusive rock - - 17 Bedrock Structure 17 Regional setting --- 17 Loco I structure - 18 ENGINEERING PROPERTIES OF GEOLOGIC UNITS - 20 Genera I ------- 20 Physical Properties - 20 Hardness 20 Joint development 20 Bedding distinctness --- 22 Foundation strength - - - 22 iii Excavation difficulty 22 Cutbank stability 24 Slope intensity ----- 24 Infi ltration rote - 25 Landfi II potentia I --- 25 Septic-tank capacity of soils - - 25 Regolith 26 Thickness on steep slopes - 26 Thickness on gentle slopes - - - 27 Clay content --- 27 Si It content - 27 Expansion-contraction 28 Drainage - 28 Over land flow - 28 Sha I low subsurface flow 28 Deep subsurface flow 29 Soils 29 Purpose - 29 General - 29 Systems of soils classification - 30 Distribution ----- 30 MINERAL RESOURCES - 38 General 38 Aggregate ­ 38 General 38 Sources 38 Recommendations --- 39 Metallic and Nonmetallic - 42 General --- 42 Reserves -- 42 Recommendations 43 Ground Water 43 General -- 43 Geologic units ---- 46 Surficial geologic units 46 Metamorphic rock units 46 Volcanic rocks -- 46 Sedimentary rocks 46 Intrusive rocks 49 Recommendations 49 GEOLOGIC HAZARDS 50 General 50 Mass Movement 50 General - 50 Causes 50 Downslope gravity component - 50 Shear resistance - - - - 50 Distribution -- 51 Impacts ---- 51 Areas of special concern 54 Recommendations 54 Slope Erosion - 56 General --- 56 iv Methods of ·study - 56 Impacts - 57 Areas of specia I concern - 57 Recommendations - 57 High Ground Water and Pending - 58 General 58 Causes - 58 Distribution 58 Impacts - 59 Recommendations - 59 Stream Flooding 60 General 60 Causes - 61 Distribution 62 Impacts - 62 Recommendations - 64 Stream Erosion and Deposition 64 General 64 Distribution 68 Torrentia 1-flood channe Is - 68 Low land-flood channe Is 68 Recommendations - 69 Earthquakes - 73 General 73 Earthquake potentia I - 73 Impacts - 75 Recommendations - 75 Bl BLIOGRAPHY 77 GLOSSARY 83 ILLUSTRATIONS Figures 1. Suggested use of this bulletin in land use decision making - 3 2. Index map of study area showing quodrong le map coverage 4 3. Time distribution of geologic units 8 4. Quaternary older alluvium (Qoa) along Anderson Creek 9 5. Patterned ground overlying Quaternary bench gravel {Qbg) 11 6. Pliocene basalt {Tpb) overlying moderate ly steep slopes of Eocene sedi men tory rock (T es) - 11 7. Southern Bear Creek va I ley - -- - 12 8. Resistant cliffs of Eocene sedimentary rock {Tes) in southeast Bear Creek valley 13 9. Metamorphosed volcanic rock of the Applegate Formation {"Rav) along the Applegate River 15 10. Regional geology of southwestern Oregon 18 11. Blocky, moderately spaced joints in granodiorite {KJd) --- 23 12. Distinct bedding in Eocene sedimentary rock {Tes) of southern Bear Creek valley 23 13. Thick silty and sandy regolith in deeply weathered granodiorite (KJd) near Ashland 26 14. Guide for the textural classification of soi ls 31 15. Rubbly Eocene and Oligocene volcanic rock {Teov) near Brownsboro ­ 39 16. Land-management analysis in areas of critical moss-movement terrain 55 17. Rogue River at Shady Cove during 1964 flood 65 18. Brownsboro after 1964 flood 65 19. Gold Ray {Roy Gold) bridge during 1964 flood - 66 20. Bear Creek in Medford during 1964 flood 66 21 . Alder Park Estates dow nstream from Gold Ray {Ray Gold) along the Rogue River during 1964 flood - -- 67 22. Rogue River near community of Rogue River during 1964 flood 67 23. Stream-bank erosion with characteristic bar formation ---- 69 24. Stream-bank erosion caused by 1964 flood 70 25. Road washed out by 1964 flood 70 26. Mountain road washed out by 1964 flood 71 27. Damage caused by 1964 flood to north approach of Bybee bridge -- 71 28. Damage to residence along Butte Creek in Lake Creek district during 1964 flood 72 29. Erosion and deposi tion caused by 1964 flood in Lake Creek district - - 72 Tab les 1. Climatic data, Jackson County, Oregon - 5 2. Populations of major communities of centra I Jackson County, Oregon 6 3. Engineering properties of geologic units, centra I Jackson County, Oregon 21 Unified Soil Classification System 32 5.4. American Association of State Highway Officials (AASHO) Soi ls Classification 33 6. Comparison of three systems of partic le-size classification 34 7. Bed rock and soi I associations of centro I Jackson County, Oregon 8. Aggregate potential of geologic units, central Jockson County, Oregon 36 9. Metallic and nonmetallic mineral resources of central Jackson County, Oregon 40 10. Representative water we lis for centro I Jackson County, Oregon - . 4744 11. Mass movement in central Jackson County, Oregon 52 12. Slide potential of geologic units ---------- 53 13. Flood discharge and frequency data, Rogue River, Applegate River, and Bear Creek 63 14. Seale of earthquake intensities and magnitudes - --- 74 15. Earthquakes felt in Jackson County, Oregon 76 VI Maps in envelope Geologic map of the following quadrangle: Medford Geologic maps of parts of the following quadrangles: Ash land and Lake Creek Gold Hi II Ruch and Wimer Trai I and Talent Geologic hazards map of the following quadrangle: Medford Geologic hazards maps of parts of the following quadrangles: Ash land and Lake Creek Gold Hi II Ruch and Wimer TraiI and Talent LAND USE GEOLOGY OF CENTRAL JACKSON COUNTY, OREGON INTRODUCTION Pu rpose Effective land use planning and land management require on adequate data base with regard to the potential uses and limitations of the land. The purpose of this study is to provide practical information on specified geologic hazards and engineering geology conditions of central Jackson County. The need for comprehensive, systematic, and reliable information of this sort has gained wide recogni­ tion by State officials, County officials, planners, private citizens, and resource specialists and is articu­ lated in Goal 7 of the Land Conservation and Development Commission. Legal trends in recent years have been toward placing increasing emphasis on comprehensive plans in land use decisions in Oregon (Fasano; Baker v. Milwaukee; Green v. Hayward). The nationwide trend is also toward the placing of greater responsibilities on permit-granting agencies. Ac know I edg men ts The author greatly appreciates the cooperation and help given by many individuals and organiza­ tions in the preparation of this report. The investigation was funded in parts by grants from the Land Conservation and Development Commission to Jackson County and also o grant from Jackson County. The grants were implemented on o matching basis by the Oregon Deportment of Geology and Mineral Industries. Special thanks ore extended to Robert Br itzemon, Jackson County Planning Director, and Curtis D. Weaver, Senior Planner. The Jackson County Planning Department, the U. S. Geological Survey (Port land office), the U. S. Soil Conservation Service, and the Oregon Water Resources Deportment supplied valuable information in their respective areas. Staff members of the Oregon Deportment of Geology and Mineral Industries assisting in the project included Steven R. Renaud, Charles A. Schumacher, Wendy John, and Rose Reed, cartographers; Beverly F. Yogi, geologist-editor; Ainslie Bricker, editor; and Ruth E. Pavlot, typist. How to Us e General Proper land management and land use planning addresses the characteristics of the land. In addition to County and city planners, the category of land use planners and managers to some degree also includes developers; pol icy formulators on the not ionol, state, and local I eve I; land holders; architects; engineers; and natural resource specialists. This bulletin provides planners in Jackson County with o synthesis of present thinking on geologic hazards and