USGS science for a changing world Active Tectonics of the Devils Mountain Fault and Related Structures, Northern Puget Lowland and Eastern Strait of Juan de Fuca Region, Pacific Northwest U.S. Geological Survey Professional Paper 1643 U.S. Department of the Interior U.S. Geological Survey Availability of Publications of the U.S. Geological Survey Order U.S. Geological Survey (USGS) publications from the Documents. Check or money order must be payable to the offices listed below. Detailed ordering instructions, along with Superintendent of Documents. Order by mail from— prices of the last offerings, are given in the current-year issues of the catalog "New Publications of the U.S. Geological Survey." 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Blakely, and Jonathan R. Childs U.S. Geological Survey Professional Paper 1643 Prepared in cooperation with the Geological Survey of Canada U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey Charles G. Groat Director Version 1.0 First printing 2001 For sale by U.S. Geological Survey, Information Services Box 25286, Federal Center Denver, CO 80225 Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government Library of Congress Cataloging-in-Publication Data Active tectonics of the Devils Mountain Fault and related structures, northern Puget Lowland and eastern Strait of Juan de Fuca region. Pacific Northwest / by Samuel Y. Johnson ... [et al.]. p. cm. - (U.S. Geological Survey professional paper; 1643) Includes bibliographical references. 1. Faults (Geology)—Juan de Fuca, Strait of, Region (B.C. and Wash.) 2. Geology—Juan de Fuca, Strait of, Region (B.C. and Wash.). I. Johnson, Samuel Y. II. Series. QE606.5.J83 A37 2002 551.8'09797—dc21 2001033439 ISBN=0-607-97457-5 Contents Abstract................................................................................................................................................. 1 Introduction........................................................................................................................................... 1 Acknowledgments............................................................................................................................... 1 Geologic Setting................................................................................................................................... 2 Seismic-Reflection Surveys—Data Acquisition and Processing................................................ 6 Stratigraphy and Seismic Stratigraphy............................................................................................ 7 Pre-Tertiary Basement Rocks................................................................................................... 7 Tertiary Sedimentary Rocks...................................................................................................... 7 Uppermost Pliocene(?) to Pleistocene Strata........................................................................ 7 Onshore Stratigraphy........................................................................................................ 7 Offshore Stratigraphy........................................................................................................ 9 Identification and Age of the Base of the Uppermost Pliocene(?) to Pleistocene Section...................................................................................................... 9 Uppermost Pleistocene and Holocene Strata........................................................................ 9 Seismic-Reflection Profiles................................................................................................................ 9 U.S. Geological Survey Line 176............................................................................................... 11 U.S. Geological Survey Line 177............................................................................................... 11 U.S. Geological Survey Line 167-168....................................................................................... 11 U.S. Geological Survey Line 166............................................................................................... 12 Industry Line 1.............................................................................................................................. 13 U.S. Geological Survey Line 165............................................................................................... 13 U.S. Geological Survey Line 164............................................................................................... 13 U.S. Geological Survey Line 162............................................................................................... 13 U.S. Geological Survey Line 158............................................................................................... 14 Industry Line 2.............................................................................................................................. 14 Geological Survey of Canada Line 15...................................................................................... 14 SHIPS LineJDF4.................................................^ 14 Industry Line 3.............................................................................................................................. 14 Geological Survey of Canada Line 37...................................................................................... 15 Geological Survey of Canada Line 35...................................................................................... 15 Evidence for Faulting Onshore, Whidbey and Camano Islands................................................... 15 Devils Mountain Fault................................................................................................................. 17 Location............................................................................................................................... 17 Outcrops.............................................................................................................................