GEOLOGIC MAP OF WASHINGTON­ SOUTHWEST QUADRANT by TIMOTHY J. WALSH, MICHAEL A. KOROSEC, WILLIAM M. PHILLIPS, ROBERT L. LOGAN, and HENRY W. SCHASSE WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES GEOLOGIC MAP GM-34 1987 WASHJNGl'ON STATE DEPARTMENT OP , • Natural Resources llr1an Boyle • Commwloner ot Publlc Landt Alt Sl8arnl • Sllpervlsor OivlSlon ot Geo!~ and Earth Reso\llCeS Raymond Lasmanls. Stale Geologlsl WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Raymond Lasmanis, State Geologist GEOLOGIC MAP OF WASHINGTON­ SOUTHWEST QUADRANT by TIMOTHY J. WALSH, MICHAEL A. KOROSEC, WILLIAM M. PHILLIPS, ROBERT L. LOGAN, and HENRY W. SCHASSE WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES GEOLOGIC MAP GM-34 1987 Bnan Boyle Comm1ss1oner ol Public Lands Art Stearns Supervisor Photograph on envelope: Mount St. Helens, March 25, 1987. View from the north; Mount Hood (Oregon) in the background. Washington Department of Transportation photo. This report is for sale by: Publications Washington Department of Natural Resources Division of Geology and Earth Resources Mail Stop PY-12 Olympia, WA 98504 Price $5.53 (folded) Tax _£ (Washington residents only) Total $6.00 Mail orders must be prepaid; please add $1.00 to each order for postage and handling. Make checks payable to the Department of Natural Resources. A limited number of flat sheets is available. Contact the Division for price information. Printed in the United States of America. ii CONTENTS Page Preface ..................................................................................................................................................... V Introduction ................................................................................................................................................. 1 Map design .................................................................................................................................................. 1 Map compilation .......................................................................................................................................... 1 Supporting data ..................................................................................................................... 1 Acknowledgments . ........... 2 Descriptions of map units .......................................................................................................................... 3 Correlation diagram .................................................................................................................................... 3 List of named units................................... .. .................... .. .. .. ........... .. .................. 4 Sources of map data ................................................................................................................................. 5 Stratigraphic columns ... ....... .... .. ....... .. ................................................................................................ 5 References cited ........... 22 Errata ..................................................................................................................... 28 ILLUSTRATIONS Figure 1. Map showing counties in southwestern Washington. ............................................... 5 figure 2. Index to sources of map data, scales 1: 1,200 through 1:24,000 and source references without maps................................................ .. .............. .. 6 figure 3. Index to sources of map data, scales 1:31,680 through 1:60,500..... .................... 7 Figure 4. Index to sources of map data, scales 1:62,500 through 1 :90,000 ... .. .... .. ......... ... ..... 8 figure 5. Index to sources of map data, scale 1: 100,000 . ..... .. .. .. .. .. .. .. .. ... ............. .. .. 9 figure 6. Index to sources of map data, scales 1:125,000 through 1:540,000... ................. 10 TABLE Table 1. Compiler, quadrangle, and Division open-file report number···········-················· ···········---· 2 iii Preface PREFACE State geologic maps are a valuable resource for educa­ Considerable new detailed and reconnaissance geologic tion, planning, mineral and energy exploration, and evaluation mapping, was done by the staff of the Division of Geology and of geologic hazards. Providing up-to-date statewide geologic Earth Resources in areas where no adequate geologic map­ mapping to the public is one of the most important functions ping existed. These areas are shown on Figure 5, and the of our state geological survey. geology is presented in more detail in the 1: 100,000-scale Previous geologic maps of Washington were published in open-file reports. 1936 by the Division of Geology (Culver, 1936) and in 1961 We have attempted to make this geologic map useful at by the Division of Mines and Geology (Huntting and others, several levels of detail and to a variety of users in the 1961), both at a scale of 1 :500,000. When we began planning following ways: (1) by publishing the map at a larger scale for the new state geologic map in 1982, the first of these than previous state geologic maps of Washington; (2) by maps was no longer available and the second was soon to be employing time-lithologic units on the map rather than forma­ out of print. Not only were state geologic maps becoming tions; (3) by portraying unconsolidated deposits in as much unavailable, but, since the last map was compiled, the plate detail as bedrock units; (4) by using a multiple-level scheme of tectonic theory had caused a revolution in geologic thinking. colors, patterns, and symbols to portray the geologic units; The fact that more than 60 percent of all Washington geologic and (5) by providing a fuller range of supporting materials maps had been published after 1960 further emphasized the than is commonly found on state geologic maps. need for a new state map. Now (September 1987) 71 percent The organization of colors, patterns, and symbols empha­ of the 927 published and thesis maps on Washington postdate sizes the time and lithologic divisions and provides map users the 1961 state map. The wealth of new geologic data was also with increasingly detailed levels of geologic information. The an important factor in our decision to publish the new state first level of detail is expressed by broad color ranges that geologic map at the expanded scale of 1:250,000. distinguish five basic rock types-Quaternary sediments, sedi­ This map is the first of four quadrant maps which, mentary rocks, metamorphic rocks, extrusive igneous rocks, together, will present the geology of the entire state of Wash­ and intrusive igneous rocks. On the second level, variations of ington. Work on the northeast quadrant is under way. The color within each broad color range indicate age. At the third southeast and northwest quadrants will follow in that order. level of detail, small groups of lithologic units are distinguished We plan to have all the quadrants available by 1993. by changes in types of pattern-for example, acidic, interme­ As noted in the section titled Map Compilation, the diate, and basic intrusive igneous rocks. The most detailed geology portrayed on this map was first compiled at a scale of lithologic distinctions are made by changes in symbol. This 1: 100,000. We chose to compile at that scale in order to scheme will enable map users to see, at a glance, broad establish a statewide map base that could preserve most of lithologic relationships, and, on closer inspection, correlate the detail of 1 :24,000- and 1 :62,500-scale source maps while, units, make tectonic interpretations, or discern the broad at the same time, consolidating the source maps to achieve a aspects of geologic history across the quadrant and ultimately more regional view. across the entire state. In order to acquire geologic mapping in unmapped or We have tried to accommodate a variety of map users in inadequately mapped areas and to substantiate geologic inter­ several ways. First, where surficial units are predominant, we pretations, the Division instituted a program to fund geologic show the surficial geology in as much detail as the bedrock, so mapping by graduate students and professors and established engineering geologists, for example, should find the map budgets for age dating and geochemistry. Since the 1984 field useful in more than a cursory way. Second, we used time­ season we have supported 36 graduate students and profes­ lithologic units rather than formations on the map to make the sors statewide, and in the southwest quadrant we have ac­ map easier to interpret and to allow those· who are not quired 32 potassium-argon (K-Ar) dates, 2 radiocarbon dates, familiar with Washington geologic names to understand and and 253 whole-rock geochemical analyses. Many of the K-Ar use the geologic data with a minimum of effort. Third, those dates were supported by Rockwell Hanford Operations (now who are accustomed to dealing with formational map units Westinghouse Hanford Co.) through S. P. Reidel. These data instead of time-lithologic units will be aided by the supporting are reported, in detail, in the 1: 100,000-scale open-file re­ material on Sheet 2: the Descriptions of Map Units lists ports. In addition, we have entered into a COGEOMAP named geologic units that are included in each of the time­ (COoperative GEOiogic MAPping) agreement with the U.S. lithologic units; the Correlation Diagram shows the age Geological Survey to map the geology of the Mount Baker, ranges of named units as well as time-lithologic units; and the Robinson Mountain,