QUATERNARY FAULTING OF DESCHUTES COUNTY, OREGON HUMBOLDT STATE UNIVERSITY By John M. Wellik A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment Of the Requirements for the Degree Master of Science Environmental Systems: Geology May, 2008 QUATERNARY FAULTING OF DESCHUTES COUNTY, OREGON HUMBOLDT STATE UNIVERSITY By John M. Wellik Approved by the Master's Thesis Committee: ________________________________________________________________________ Mark A. Hemphill-Haley, Geology Professor Date ________________________________________________________________________ Raymond M. Burke, Committee Member Date ________________________________________________________________________ John D. Longshore, Committee Member Date ________________________________________________________________________ Sharon L. Brown, Graduate Coordinator Date ________________________________________________________________________ Chris A. Hopper, Interim Dean Date Research, Graduate Studies & International Programs ABSTRACT QUATERNARY FAULTING OF DESCHUTES COUNTY, OREGON John M. Wellik Sixty-one normal faults were identified in a 53-kilometer long by 21-kilometer wide northwest-trending zone in central and northern Deschutes County, Oregon. The faults are within the Tumalo and Sisters fault zones and the Northwest Rift Zone, and extend from Newberry Volcano to Black Butte. Faults are identified in and near the population centers of Bend, Redmond, Sisters, and Tumalo. The investigation identified displacement of volcanic flows dated at 24 ± 14 ka using K/Ar and 39 ± 6 ka using 40Ar/ 39Ar, displacement of several prominent pyroclastic deposits, displacement of multiple undated volcanic flows, and displacement of undated sedimentary deposits; 7,000-year- old Mazama ash is unfaulted. Displacement of deposits in the southern portion of the study area relative to displacement in the northern portion is interpreted having occurred more recently and is generally of greater magnitude. Evidence of fault reactivation over time was found, as older rock units are displaced more than younger ones along the same segment of a fault. iii ACKNOWLEDGEMENTS Many thanks and eternal indebtedness to the following: Deschutes County personnel and residents, Deschutes County Commissioners office, Deschutes County Commissioner Dennis Luke for establishing project financing, Deschutes County Geographical Information Systems Department, Deschutes National Forest employees Larry Chitwood and Bob Jensen, Humboldt State University Geology Department professors and staff, Bud Burke, Mark Hemphill-Haley, John Longshore, Susan Cashman, Harvey Kelsey, Humboldt State University fall 2002 Quaternary Field studies class (Geo 554), Ian and Bonnie (Mrs.) Pryor, Diane Sutherland, Michelle Roberts, Ronna Bowers, Jay Stallman, Todd Williams, Jay Patton, Rick Murphy, LACO Associates, my dad and sisters, especially Beth for hiking with me, and Barb and Jim Wenzinger. Thebe was a great field companion. Thanks to Cynthia Werner and Sharon Brown for guiding me through paper formatting and with editing help. A special note of thanks to my lovely wife Anne for her seemingly limitless patience, love, support, care, inspiration and constant encouragement; I would not be writing this section without her. I love you Anne. Dean, you mean the world to me; I hope this provides a good example. Here it is mom. iv TABLE OF CONTENTS ABSTRACT................................................................................................................. iii ACKNOWLEDGEMENTS......................................................................................... iv TABLE OF CONTENTS...............................................................................................v LIST OF TABLES...................................................................................................... vii LIST OF FIGURES ................................................................................................... viii LIST OF APPENDICES................................................................................................x INTRODUCTION .........................................................................................................1 Geologic Setting.................................................................................................2 Previous Work ...................................................................................................4 METHODS ....................................................................................................................6 DEPOSITS.....................................................................................................................8 Quaternary Deposits.........................................................................................10 Tertiary Deposits..............................................................................................14 TUMALO AND SISTERS FAULT ZONES AND THE NORTHWEST RIFT ZONE .....................................................................15 Tumalo Fault Zone...........................................................................................15 Sisters Fault Zone ............................................................................................16 Bend Area Faults..............................................................................................17 Northwest Rift Zone ........................................................................................17 Map Scale Fault Descriptions ..........................................................................18 Outcrop Scale Fault Description......................................................................19 v Relation of Faults and Volcanic Edifices.........................................................20 Evidence of Fault Timing ................................................................................22 Evidence of Fault Reactivation........................................................................25 DISCUSSION..............................................................................................................27 SUMMARY AND CONCLUSIONS ..........................................................................30 ADDITIONAL GEOLOGIC QUESTIONS AND STUDY OPPORTUNITIES ........31 TABLES ......................................................................................................................32 FIGURES.....................................................................................................................36 PHOTOGRAPHS ........................................................................................................48 REFERENCES ............................................................................................................58 vi LIST OF TABLES Table Page 1. Fault Data…………………………………………………………….………….. 33 2. Fault and Stratigraphy Matrix…………………………………………………… 34 vii LIST OF FIGURES Figure Page 1. Study Area Map…………………………………………………………………... 37 2. Regional Geologic Structures Relative to the Study Area………………………... 38 3. Correlation of Rock Units………………………………………………………… 39 4. Tumalo Fault Zone………………………………………………………………... 40 5. Sisters Fault Zone………………………………………………………………….41 6. Bend Area Faults…………………………………………………………………..42 7. Northwest Rift Zone…………………………………………………………….....43 8. Photograph Legend………………………………………………………………...44 9. Volcanic Structures Relative to Study Area Faults……………………………….. 45 10. Potential Tertiary Cinder Cones and Flow Lobes near Tumalo Reservoir…….. ..46 11. Log of a portion of the south wall of the Tumalo fault exploratory trench (TT1). 47 Photograph Page 1. Fault T7 in Quaternary sand at southeastern corner of the intersection of Highway 126 and Cloverdale Road………..…………………………………………………... 49 2. Fault T19 in Quaternary basalt flows of Newberry Volcano in southern Bend; three- story house built on up-thrown side for scale………………………………………...49 3. Fault S6 in Tertiary Deschutes formation lava flows parallel to Barr Road, north of Tumalo……………………………………...……………………….………………. 50 4. Fault B2 in Quaternary basalt of Newberry Volcano, south of Bend near Horse Butte……………………………………...……………………………………….…. 50 viii 5. Fracture in Quaternary Tumalo Tuff with fracture fill from the overlying gravel deposit along the Tumalo Fault (T1)….……………….……………………………. 51 6. Silica-lined fracture in up-thrown (western) side of fault T7 at Cloverdale and Highway 126………………………………………………………...…………......... 52 7. Vertical fractures in Quaternary Shevlin Park Tuff (Qsp) in Anderson pit in Bend. ………………………………………………………………………………..………53 8. Fault S10 in Quaternary Tumalo Tuff exposed in a borrow pit parallel to Tumalo Market Road……………...………………………………………………….……….54 9. Fault T19 in Quaternary Tumalo Tuff at Anderson Pit in Bend...………………. 55 10. Fault B4 in Quaternary basalt of Newberry Volcano south of Knott Landfill in southern Bend...……………………….………………………………….…………..55 11. Fault B4 transects Highway 20 in central Bend, with cars for scale. White car is on the up-thrown (western) side of the fault…………………………………………... 56 12. Fault T1, the Tumalo Fault, in Quaternary sand and Tertiary Deschutes formation lava flows at Bull Flat……………………………………………………………….. 56 13. Fault B3 in Quaternary andesitic basalt of Pilot Butte, northeast of Pilot Butte in Bend………………………………………………………………………..………... 57 14. Fault S16 in Tertiary Deschutes formation pyroclastic flow deposits and lava flows. ………………………………………………………………………………………..57 Map Plates 1 and 2. Tumalo and Sisters Fault Zones Map and cross-sections.....Back