ACTIVE FAULTING AND QUATERNARY PALEOHYDROLOGY OF THE TRUCKEE FAULT ZONE NORTH OF TRUCKEE, CALIFORNIA By Aaron Dwight Melody A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment of the Requirements for the Degree Master of Science In Environmental Systems: Geology September, 2009 ACTIVE FAULTING AND QUATERNARY PALEOHYDROLOGY OF THE TRUCKEE FAULT ZONE NORTH OF TRUCKEE, CALIFORNIA By Aaron Dwight Melody Approved by the Master's Thesis Committee: Dr. Mark Hemphill-Haley, Major Professor Date Dr. Brandon Schwab, Committee Member Date Thomas Sawyer, Committee Member Date Dr. Chris Dugaw, Graduate Coordinator Date Dr. John Lyon, Dean for Research and Graduate Studies Date ABSTRACT ACTIVE FAULTING AND QUATERNARY PALEOHYDROLOGY OF THE TRUCKEE FAULT ZONE NORTH OF TRUCKEE, CALIFORNIA By Aaron Dwight Melody, Master of Science, Geology Active faulting has been documented along the northwest-striking Mohawk Valley fault zone (2-3 normal-dextral rupture events in the Holocene with geologic slip rates of ~0.2mm/yr) and in the Lake Tahoe basin (mostly on north-striking normal faults with geologic slip rates of up to 0.4 mm/yr). Evidence for Holocene faulting in the region between these zones; for example along the Truckee fault zone, has been sparse to absent. Soil cores and trenches were hand-dug in a meadow north of Truckee, California bound by a low (~1m) north-south trending, east-facing scarp. Radiocarbon age estimates of organic sediment indicate the meadow was a marsh during the Late Quaternary and was abruptly infilled and/or desiccated with the deposition of the ~7,000 yr B.P Tsoyowata tephra (Mt. Mazama). Both the tephra and the marsh sediment are offset ~50-100 cm across a vertical fault striking sub-parallel with the scarp. This study provides evidence for at least one surface-faulting event during the Holocene and possibly another in the late Pleistocene along the Truckee fault zone. These findings may aid in the identification of other seismic sources capable of significant ground rupture in the area. iii ACKNOWLEDGEMENTS This project was supported by the U.S. Army Corps of Engineers (Ronn Rose) and the U.S. Bureau of Reclamation (Larry Anderson) - both of whom readily offered support. Without their contributions, this investigation would have stopped at conjecture. The Truckee Ranger Station granted access to U.S. Forest Service Lands. A huge thanks to Roland Rueber, Mike Foget, Pat Barsanti, Erik Nielsen, John Aveggio, Shane Beach, Tom Stephens, Gary Simpson, Anson Call, Dave Bradley, Greg Williston, Joe Aufdermauer, Dave Gonzales, and all the staff at SHN Consulting Engineers and Geologists, Inc. in Eureka, CA. SHN provided respectable employment during the entire course of this endeavor. Guidance and encouragement are greatly appreciated from Dr. Mark Hemphill-Haley, Dr. Brandon Schwab, Dr. Bud Burke, Dr. Sue Cashman, Dr. Ken Aalto, and the entire HSU Geology Department staff. I would also like to thank the premier northern Sierran tectonic geologist Thomas Sawyer. He, more than anyone, encouraged me to keep on even in the early days of abundant auger refusal and volcanics everywhere. “Keep looking,” he said. A very heartfelt thanks to Beau Whitney, Christopher Slack, Ronna Bowers, Martha Mitchell, and Tami Darden for help in trench digging during the inaugural pre-FOP (2006)! Thanks to Alan Ramelli, Rich Koehler, Joanna Redwine, Peter Birkeland, Chris Henry, and Chad Pritchard for many thought- provoking conversations. Despite not understanding the attraction to digging in the dirt, I thank my parents, who supported me 100%. My wife Kathryn accompanied many field excursions to the meadow and I thank her for her faith in me and patience in this process. iv TABLE OF CONTENTS Page ABSTRACT ...................................................................................................................... iii ACKNOWLEDGEMENTS ............................................................................................... iv TABLE OF CONTENTS ....................................................................................................v LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES ........................................................................................................... ix LIST OF APPENDICES ......................................................................................................x INTRODUCTION ...............................................................................................................1 Tectonic Setting ...................................................................................................... 4 Cummulative Dextral Motion ..................................................................... 5 Truckee Fault zone ...................................................................................... 6 Geodetics................................................................................................................. 8 Bedrock Geology .................................................................................................... 9 Pre-Miocene Rocks ................................................................................... 10 Miocene-Pleistocene Volcanics ................................................................ 10 Pliocene Deposits of Boca Basin and Verdi Range Uplift ....................... 17 Prosser Creek Alluvium ............................................................................ 20 Pleistocene Glaciations ......................................................................................... 21 Hobart Glaciation ...................................................................................... 22 Donner Lake Glaciation ............................................................................ 23 Tahoe Glaciation ....................................................................................... 23 v Tioga Glaciation ....................................................................................... 24 Outwash Terraces .................................................................................................. 25 Sagehen Creek Terraces ............................................................................ 25 METHODS ........................................................................................................................27 Air Photo and Topographic Analyses ................................................................... 30 Lithostratigraphic Descriptions ............................................................................. 30 Textural Analysis .................................................................................................. 30 Hand-Excavated Soil Coring ................................................................................ 31 Hand-Excavated Soil Pits and Trenches ............................................................... 31 Tephra Analysis .................................................................................................... 32 Radiocarbon Dating .............................................................................................. 32 Correlation of Pre-Holocene Deposits .................................................................. 33 STUDY AREA MEADOW STRATIGRAPHY ...............................................................34 Textural Analysis .................................................................................................. 35 Tephra Glass Composition .................................................................................... 44 Radiocarbon Age Estimates .................................................................................. 44 Pit HM-Pit-............................................................................................................ 45 Pit HM-Pit-03........................................................................................................ 46 Pit HM-Pit02 ......................................................................................................... 47 Pit HM-Pit-02-North Wall ........................................................................ 48 Pit HM-Pit-02-South Wall ........................................................................ 50 Hand Auger Cores................................................................................................. 52 DISCUSSION ....................................................................................................................55 vi Paleohydrology ..................................................................................................... 55 Most-Recent Rupture Event .................................................................................. 56 Penultimate Event ................................................................................................. 58 CONCLUSION ..................................................................................................................60 REFERENCES ..................................................................................................................62 APPENDIX A TEXTURAL ANALYSIS RESULTS .....................................................70 APPENDIX B TEPHRA ANALYSIS RESULTS ...........................................................71 vii LIST OF TABLES Table Page 1 Radiocarbon Age Estimates .........................................................................................