U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Geologic map of the East Canyon Ridge quadrangle, southern Cascade Range, Washington by Donald A. Swanson1 Open-File Report 94-591 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 'U.S. Geological Survey, Department of Geological Sciences AJ-20, University of Washington, Seattle, Washington 98195 CONTENTS INTRODUCTION ............................. 1 FIGURES ACKNOWLEDGMENTS ....................... 1 1. Map showing location of East Canyon Ridge ROCK TERMINOLOGY AND CHEMICAL quadrangle relative to other quadrangles and the CLASSIFICATION .......................... 2 Southern Washington Cascades Conductor .... 2 GEOLOGIC OVERVIEW OF QUADRANGLE ...... 7 2. Map of East Canyon Ridge quadrangle, showing TERTIARY ROCKS OLDER THAN INTRUSIVE localities mentioned in text ................. 3 SUTTEOFKIDDCREEK..................... 8 3. Total alkali-silica classification diagram for rocks in Volcaniclastic rocks (map unit Ttv) ............. 8 East Canyon Ridge quadrangle .............. 3 Lava flows and domes ........................ 9 4. Plot of phenocryst assemblage vs. SiO2 for rocks in Intrusions ................................. 10 East Canyon Ridge quadrangle .............. 6 Dikes .................................. 10 5. Locations of samples collected in East Canyon Ridge Plugs and other intrusions ................. 10 quadrangle ............................. 6 Silicic intrusions ......................... 11 6. Alkali-lime classification diagram for Tertiary RHYOLITE INTRUSION OF SPUD HILL ........ 12 rocks in East Canyon Ridge quadrangle ....... 6 OTHER SILICIC INTRUSIONS ............... 12 7. Plot of FeO*/MgO vs. SiO2 for rocks in East Can­ INTRUSIVE SUITE OF KIDD CREEK ........... 13 yon Ridge quadrangle ..................... 7 STRUCTURE ............................... 13 8. Plot of total alkalies vs. SiO2 for rocks in East Folds ................................... 13 Canyon Ridge quadrangle .................. 7 Faults and shear zones ....................... 14 9. Plot of KjO vs. SiO2 for rocks in East Canyon Steep dips west of Spud Hill .................. 15 Ridge quadrangle ........................ 7 Pin Creek zone ............................ 15 10. Distribution of andesite dikes, silicic rocks, and QUATERNARY LAVA FLOWS AND VENT axial traces of folds in mapped quadrangles ... 11 DEPOSITS ............................... 16 11. Rose diagrams of strikes of dikes and beds in East Dacite of Olallie Lake ................:...... 16 Canyon Ridge quadrangle ................. 12 Dacite of Sheep Creek ....................... 16 12. Generalized map showing distribution of intrusive Basalt and basaltic andesite of Potato Hill ....... 17 suite of Kidd Creek ...................... 14 Basalt of Juniper Creek and related basalt........ 17 13. Plots of TiO2, FeO*, and MnO vs. SiO2 for rocks Basalt of East Canyon Creek ............... 18 in East Canyon Ridge quadrangle ........... 15 Basalt west of Spud Hill ................... 19 14. Map showing basalt of Juniper Creek and chemical Eruptive conditions ...................... 20 correlatives relative to Pin Creek zone ....... 16 Basalt of Spring Creek ...................... 21 15. Plot of K2O content of basalt of Spring Creek vs. QUATERNARY SEDIMENTARY DEPOSITS ..... 20 distance from vent ...................... 19 Glacial deposits ............................ 20 Landslide deposits .......................... 21 TABLES Old landslide ........................... 21 1. Chemical analyses .......................... 4 DESCRIPTION OF MAP UNITS ................ 22 2. Radiometric ages .......................... 20 REFERENCES CITED ........................ 28 CORRELATION OF MAP UNITS ............... 30 PLATES EXPLANATION OF MAP SYMBOLS ........... 31 1. Geologic map ................... Separate sheet 2. Geologic cross sections ............ Separate sheet Geologic map of the East Canyon Ridge quadrangle, southern Cascade Range, Washington by Donald A. Swanson INTRODUCTION ence on the geology of the area. All quadrangles that I have The East Canyon Ridge 7.5-minute quadrangle is cen­ studied lie either within the SWCC or astride its margin. tered about 40 km east-northeast of Mount St. Helens, 15 km The East Canyon Ridge quadrangle drains principally northwest of Mount Adams, and 12 km west of the crest of into the Cispus River (fig. 2), a trunk stream carrying water the Cascade Range in southern Washington (fig. 1). It is the from the north side of Mount Adams and the west side of the most recent in a series of adjoining quadrangles that I have rugged Goat Rocks Wilderness into the Cowlitz River. The studied geologically. Geologic maps and accompanying de­ Lewis River drains the southern part of the quadrangle and tailed text have been open-filed for the French Butte, Green­ flows directly into the Columbia River. East Canyon Creek horn Buttes, Tower Rock, McCoy Peak, and Blue Lake is a major stream in the quadrangle; for this paper, it is di­ quadrangles (Swanson, 1989, 1991, 1992, 1993) and vided into upper and lower segments, the upper flowing finished but not yet compiled for the Hamilton Buttes quad­ along strike to about the mouth of Summit Prairie Creek and rangle (D.A. Swanson, unpublished mapping, 1993). I plan the lower segment flowing across structure from there to its to complete the mapping of the Tertiary rocks in th^ Green mouth at the Cispus River. Mountain quadrangle in 1994; Hildreth and Fierstein (in Roads follow most major drainages in the quadrangle, press) have already mapped the Quaternary rocks there. Also and logging roads in various conditions climb some steep in 1994 I plan to map those parts of the Purcell Mountain slopes. Many of the roads are not shown on the quadrangle and Packwood quadrangles that are south of the Cowlitz map. Access is by foot trail in the upper Summit Prairie River. Richard B. Moore will be mapping north of the river, Creek-Quartz Creek-Pin Creek area. The west and northeast and a geologic map of the Randle quadrangle, prepared parts of East Canyon Ridge have neither roads nor trails. jointly with Moore and Carl Thornber, is nearly completed. Oligocene and early Miocene volcaniclastic and volcanic The geologic research in these quadrangles forms part of rocks, mainly of basaltic andesite and andesite composition an effort, which began small but over the years has become (table 1), underlie most of the quadrangle. Many Tertiary in­ a major undertaking, to understand the development of the trusions, mostly sill-like and commonly silicic, cut the Cascade arc in southern Washington from its inception in the layered rocks. Pleistocene dacite flows barely entered the late Eocene or early Oligocene. A primary goal has been to eastern part of the quadrangle from nearby vents. Late Pleis­ tie the Tertiary stratigraphy of the area near and west of tocene basalt issued, typically explosively, from several Mount St Helens (Evarts and Ashley, 1984, 1990a, 1990b, vents near Spud Hill. Late Pleistocene basalt and basaltic 1991, 1992, 1993a, 1993b, in press a and b; Evarts and andesite flooring the Cispus valley was erupted from north others, 1987; Swanson, 1989, 1991, 1992, 1993) into the of Mount Adams. now classic stratigraphic section in the Mount Rainier- Glacial drift covers large areas, but generally bedrock White Pass area defined by Fiske and others (1963; see also crops out along creeks, steep slopes, and ridges. The bed­ Waters, 1961) and modified by Vance and others (1987). rock mapping involved traverses along most drainages, large This work is establishing an improved regional geologic and small; such work finds many exposures, even in densely framework for the southern Washington Cascades and de­ forested terrain. The area is downwind from Mount St. fining a geologic research corridor across the west side of Helens but so far away that tephra is less than a few centi­ the Cascade Range (Swanson and Evarts, 1992; Evarts and meters thick and poses no problems for mapping bedrock. Swanson, 1994), from the upper Eocene marine rocks of the Previous small-scale (1:100,000 and smaller) reconnais­ Puget Lowland to the Late Jurassic-Early Cretaceous sance geologic mapping for regional purposes has included Rimrock Lake inlier (Miller, 1989) along and just east of the the East Canyon Ridge quadrangle, mainly by Hammond crest in the White Pass-upper Tieton River area and east­ (1980), Korosec (1987), and J.G. Smith (1993 and an un­ ward to the margin of the Columbia Plateau (Swanson, published map of the Yakima 2-degree sheet). A 1:24,000- 1978) (fig. 1). The ongoing study will provide geologic sup­ scale map accompanies Harle's (1974) thesis study of the port for seismic and other geophysical surveys in a corridor Council Bluff area. linking coastal Washington with the Columbia Plateau, now planned for fiscal year 1995 and possibly 1996 (Wells and ACKNOWLEDGMENTS others, 1993). Detailed field work is testing whether a Wes Hildreth, Willie Scott, and Richard Waitt offered pronounced electrical conductivity layer in the middle crust, needed advice for interpreting several features along the Cis­ the southern Washington Cascades conductor (SWCC) of pus valley. Mike Korosec kindly provided field maps and Stanley and others (1987, 1992), has a recognizable influ­ chemical analyses