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USGS Banner with Coachella Valley as seen from Keyes View in Joshua Tree National Park
Western Earth Surface Processes Team

San Andreas Fault System in the Inland Empire and Salton Trough

This website is a geology tour of the Inland Empire region of Southern California.

[Text modified from USGS Open-File Report 92-354.]

TABLE OF CONTENTS

Introduction

Summary


Major Structural Blocks

SoCal's Major Faults


Right Lateral Strike-Slip Faults Compressional Fault Systems
  • San Gorgonio Pass Fault Zone
  • Cucamonga Fault Zone
Extensional Fault Sustems
  • Normal Faults of the Coachella and Morongo Valleys
  • Beaumont Plain Fault Zone
  • Crafton Hills Horst-and-Graben Complex
  • Dip-slip Faults of the San Bernardino Valley and San Bernardino Mountains
Neotectonic Framework of the South-Central Transverse Ranges and Vicinity
  • Seismicity, Slip Rates, and Strain
  • Neotectonic Framework
  • The San Andreas Fault System in the Vicinity of the Central Transverse Ranges: a Product of Left and Right Steps in a Right-Lateral Fault Zone
 

Map of the Inland Empire region show location of areas and fault described in this report.
Map of the Inland Empire region show location of areas and fault described in this report. Click here for a larger view of the map.





Also see these geology resource pages!

Coachella Valley
Coastal Ranges
Death Valley National Park
Joshua Tree National Park
Los Angeles Basin
Mojave Desert
Peninsular Ranges
San Bernardino Basin
San Bernardino Mountains
San Gabriel Mountains
San Gorgonio Pass
Santa Barbara Coastal Plain
Transverse Ranges

SoCal's Geologic History

INTRODUCTION

The Inland Empire and Salton Trough regions of San Bernardino and Riverside Counties have numerous faults that at first glance appear to have no coherent patterns or relations to each other. However, geologic research over the last 40 years has shown that the distribution and behavior of these faults can be explained if they are viewed as components of a larger San Andreas Fault System.

The Inland Empire-Salton Trough region is geologically and seismologically the most complex part of the San Andreas Fault system in southern California. Here, several strands of the master San Andreas Fault have succeeded each other through the last 15 million years, each strand in turn continuing the inexorable northwestward movement of coastal California relative to the desert interior. Complexities in this right-lateral-shear history have caused subsidiary fault zones to develop-some sharing the right-lateral strike-slip role of the San Andreas itself, others developing where the earth's crust has been squeezed (contractional faults and fold belts) or stretched (extensional faults).

Image of San Andreas fault system
By fault system we mean a network of faults and folds whose orientation, movement style, and long-term geologic history result from the interactive nature of the entire network. Each element in the network plays a role as the earth's crust in southern California responds to stresses generated within the Pacific-North American plate boundary. The San Andreas Fault itself is just one component of this fault network. This master fault is a right-lateral strike-slip fault that is flanked by other right-slip, left-slip, contractional, and extensional fault zones and associated fold belts.

Continue to the Summary.


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