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Geological Resources

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Geological Resources NAPA COUNTY BASELINE DATA REPORT . CHAPTER 1 GEOLOGICAL RESOURCES PURPOSE UPDATE CHRONOLOGY The purpose of this chapter is to provide a NOVEMBER 30, 2005—VERSION 1 current summary of baseline geologic features and related hazards in Napa County and to provide a current map inventory of these features. This document and the data assembled provide broad tools for site and regional planning as well as the basis for future planning documents relating to the protection and management of geological resources. LANDSLIDING AND HUMMOCKY TERRAIN IN A NAPA VALLEY GRASSLAND NAPA COUNTY BASELINE DATA REPORT GEOLOGICAL RESOURCES Landslides and Soil Creep ....................................................................................................1-25 Geologic Hazards of County Subregions ..............................................................................1-26 TABLE OF CONTENTS CONCLUSIONS AND REPORT UPDATE RECOMMENDATIONS .............................................................1-27 Countywide ...........................................................................................................................1-27 INTRODUCTION ................................................................................................................................1-1 Conclusions Specific to County Subregions..........................................................................1-28 Purpose ..................................................................................................................................1-1 Update Recommendations Countywide................................................................................1-28 Limitations and Use ................................................................................................................1-1 Update Recommendations Subregion ..................................................................................1-29 POLICY CONSIDERATIONS................................................................................................................1-1 REFERENCES.................................................................................................................................1-30 Federal Policies ......................................................................................................................1-1 State Policies..........................................................................................................................1-2 Local Policies..........................................................................................................................1-3 METHODOLOGY...............................................................................................................................1-5 TABLES Definition of Study Area..........................................................................................................1-5 Technical Approach................................................................................................................1-5 1-1 Modified Mercalli Intensity Scale...........................................................................................1-16 PHYSIOGRAPHY...............................................................................................................................1-5 1-2 Significant Historic Earthquake Activity(Napa County...........................................................1-16 Physiography of Napa County ................................................................................................1-5 Physiography of County Subregions.......................................................................................1-6 1-3 Probabilistic Seismic Hazard Analysis—Three Physiographic Regions of Napa County, California ........................................................................................................1-17 BEDROCK FORMATIONS AND GEOLOGIC STRUCTURE .......................................................................1-7 1-4 Known Active Faults in Napa County....................................................................................1-18 Evolution of the Northern California Coast Ranges ................................................................1-7 Faults and Geologic Structures of Napa County.....................................................................1-7 Major Bedrock Groups in Napa County ..................................................................................1-8 MAPS SOIL DEPOSITS .............................................................................................................................1-11 Follows Page Geologic Surficial Deposits in Napa County .........................................................................1-11 Major Soil Groups in Napa County .......................................................................................1-12 1-1 Evaluation Areas...................................................................................................................1-32 1-2 Physiography ........................................................................................................................1-32 SEISMICITY....................................................................................................................................1-15 1-3 Slope.....................................................................................................................................1-32 Historic Fault Activity ............................................................................................................1-16 1-4 General Geology...................................................................................................................1-32 Probability of Future Earthquakes.........................................................................................1-16 General Probabilistic Seismic Design...................................................................................1-17 1-5 Surficial Deposits ..................................................................................................................1-32 Major Earthquake Faults in Napa County.............................................................................1-17 1-6 Soil Texture Classes .............................................................................................................1-32 Seismicity of County Subregions ..........................................................................................1-20 1-7 Engineering Properties AASHTO..........................................................................................1-32 1-8 Landslides.............................................................................................................................1-32 GEOLOGIC AND SEISMIC HAZARDS ................................................................................................1-20 Hazard Summary..................................................................................................................1-20 1-9 Flood Zones..........................................................................................................................1-32 Surface Fault Rupture...........................................................................................................1-22 1-10 Liquefaction Susceptibility.....................................................................................................1-32 Seismically Induced Ground Shaking ...................................................................................1-22 1-11 Erosion K factor.....................................................................................................................1-32 Seismically Induced Ground Failures ...................................................................................1-23 Earthquake Generated Landsliding ......................................................................................1-23 Other Earthquake Ground Failures.......................................................................................1-23 Failure of Levees and Dams.................................................................................................1-24 Ground Subsidence/Settlement............................................................................................1-24 GEOLOGICAL RESOURCES—VERSION 1, NOVEMBER 2005 -1-i- NAPA COUNTY BASELINE DATA REPORT THP Timber Harvesting Plan LIST OF ACRONYMS AND ABBREVIATIONS UBC Uniform Building Code USGS U.S. Geological Survey AASHTO American Association of State Highway and Transportation Officials Valley Napa Valley Bay Area San Francisco Bay Area BDR Baseline Data Report BMPs Best management practices Caltrans California Department of Transportation CBC California Building Code CDF California Department of Forestry County Napa County CWA Federal Clean Water Act DSA California Division of State Architect DSOD California Division of Safety of Dams EFZs Earthquake Fault Zones EIR Environmental impact report EPA U.S. Environmental Protection Agency FEMA Federal Emergency Management Agency FERs Fault Evaluation Reports g The force an earthquake applies to a structure is expressed in terms of a percentage of gravity General Permit General Permit for Storm Water Discharges Associated with Construction Activity GIS Geographic information systems Ka Thousand years ago m Meters Ma Million years ago NPDES National Pollutant Discharge Elimination System NRCA National Resources Conservation Agency NRCS Natural Resources Conservation Service
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