U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Geologic map of the Hamilton Buttes quadrangle, southern Cascade Range, Washington by Donald A. Swanson1 Open-File Report 96-0016 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, University of Washington, Department of Geological Sciences, Box 351310, Seattle, Washington 98195-1310 CONTENTS INTRODUCTION ............................. 1 FIGURES ACKNOWLEDGMENTS ....................... 2 1. Map showing location of Hamilton Buttes quadrangle ROCK TERMINOLOGY AND CHEMICAL relative to other quadrangles and the Southern CLASSIFICATION .......................... 3 Washington Cascades Conductor .......- 2 GEOLOGIC OVERVIEW OF QUADRANGLE ...... 6 2. Map of Hamilton Buttes quadrangle, showing locali­ TERTIARY ROCKS OLDER THAN INTRUSIVE ties mentioned in text ..................... 3 SUITE OF KIDD CREEK ..................... 8 3. Total alkali-silica classification diagram for rocks in Arkose of Chambers Creek (map unit Tsc) ........ 8 Hamilton Buttes quadrangle ................ 3 Significance of interbedded arkose and volcanic 4. Plot of phenocryst assemblage vs. SiO2 for rocks in sandstone ............................. 9 Hamilton Buttes quadrangle ................ 6 Relation to SWCC ........................ 10 5. Locations of samples collected in Hamilton Buttes Volcaniclastic rocks (map unit Ttv)............. 10 quadrangle.............................. 6 Lava flows (map unit Ta) .................... 11 6. Alkali-lime classification diagram for Tertiary Intrusions ................................. 12 rocks in Hamilton Buttes quadrangle ......... 6 Dikes .................................. 12 7. Alkali-lime classification diagram for Quaternary Sills (map units Taih and Tai) .............. 12 rocks in Hamilton Buttes quadrangle ......... 7 SILLS OF HUGO LAKE ................... 12 8. Plot of FeO*/MgO vs. SiO2 for rocks in Hamilton SPARSELY TO MODERATELY PLAGIOCLASE- Buttes quadrangle ........................ 7 PHYRIC SILLS ....................... 14 9. Plot of total alkalies vs. SiO2 for rocks in Hamilton Other intrusions ......................... 14 Buttes quadrangle ........................ 7 INTRUSIVE SUITE OF KIDD CREEK ........... 15 10. Plot of K2O vs. SiO2 for rocks in Hamilton Buttes STRUCTURE ............................... 15 quadrangle .............................. 7 Folds .................................... 15 11. Distribution of andesite dikes and dacite and rhyo­ Faults and shear zones ....................... 16 lite extrusions and intrusions in quadrangles PLEISTOCENE LAVA FLOWS AND SUB- south.of.CowJitz-River. ................... 13 GLACIAL CONE (TUYA) ................... 17 12. Rose diagrams showing strikes of dikes and beds Dacite of Jordan Creek (map unit Qdj) .......... 17 in Hamilton Buttes quadrangle ............. 14 Andesite, dacite, and rhyolite of Goat Ridge ...... 17 13. Plot of A12O3 vs. SiO2 for sills of Hugo Lake and Andesite of Old Snowy Mountain .............. 19 unit Tai ............................... 15 Basalt and basaltic andesite in southeastern 14. Plots of TiO2, FeO*, and MnO against SiO2 for corner of quadrangle ...................... 20 rocks in Hamilton Buttes quadrangle ........ 16 Basalt ofWalupt Lake volcano (map unit Qbw) . 20 Basalt of Two Lakes (map unit Qbt) .......... 20 Basaltic andesite (map unit Qba) ............ 20 TABLES QUATERNARY SEDIMENTARY DEPOSITS ..... 20 1. Chemical analyses of rocks in Hamilton Buttes quad­ Glacial deposits ............................ 20 rangle ................................. 4 Landslide deposits (map unit Qls) .............. 21 2. Heavy minerals in arkose of Chambers Creek ..... 9 DESCRIPTION OF MAP UNITS ................ 21 REFERENCES CITED ........................ 25 PLATES CORRELATION OF MAP UNITS ............... 28 1. Geologic map of Hamilton Buttes EXPLANATION OF MAP SYMBOLS ........... 29 quadrangle .................... Separate sheet 2. Geologic cross sections of Hamilton Buttes quadrangle.................... Separate sheet Geologic map of the Hamilton Buttes quadrangle, southern Washington Cascade Range by Donald A. Swanson INTRODUCTION Most of the Hamilton Buttes quadrangle drains into the The Hamilton Buttes 7.5-minute quadrangle is centered Cispus River (fig. 2), a trunk stream carrying water from the about 60 km northeast of Mount St. Helens, 25 km north- north side of Mount Adams and the southwest side of the northwest of Mount Adams, and 10 km west of the crest of Goat Rocks Wilderness westward into the Cowlitz River. the Cascade Range in southern Washington (fig. 1). It is the The northern part of the quadrangle drains into the Cowlitz most recent in a series of adjoining quadrangles that I have via northwest-flowing Johnson Creek and its tributaries. studied geologically. Geologic maps and accompanying de­ Roads follow most major drainages in the quadrangle, tailed text have been open-filed for the French Butte, Green­ and logging roads (a few not shown on the quadrangle map) horn Buttes, Tower Rock, McCoy Peak, Blue Lake, and East in various conditions climb some steep slopes. Access is by Canyon Ridge quadrangles (Swanson, 1989, 1991, 1992, foot trail in the northeastern part of the quadrangle (in the 1993, 1994a). In addition, I mapped that part of the Randle Goat Rocks Wilderness), along Elk Ridge, and along the quadrangle south of the Cowlitz River (Moore and others, divide from St. John Lake past Mission Mountain and south 1994). I have also finished mapping those parts of the Purcell beyond Point 5288 (fig. 2). Shorter trails enable easy access Mtn. and Packwood quadrangles south of the Cowlitz River to the south side of Hamilton Buttes, the ridge between Hugo (D.A. Swanson, unpublished mapping, 1994); this mapping Lake and Chambers Lake, and the Cispus River just below will be combined with that by R.B. Moore and N.G. Banks Mile 47. Rugged Stonewall Ridge and upper Mission Creek north of the Cowlitz. In 1995 I completed mapping the Pack- have neither roads nor trails. Some trails are not shown on wood Lake quadrangle. the quadrangle. Also note that the boundary of the Goat The geologic research in these quadrangles forms part of Rocks Wilderness is incorrect on the quadrangle; in particu­ an effort, which began small but over the years has become lar the Wilderness has been extended north and east of a major undertaking, to understand the development of the Chambers Lake. Cascade arc in southern Washington from its inception in the Late Eocene, Oligocene, and early Miocene volcaniclas- late Eocene. A primary goal has been to tie the Tertiary tic and volcanic rocks, mainly of basaltic andesite and ande- stratigraphy of the area near and west of Mount St. Helens site composition (table 1), underlie most of the quadrangle. (Evarts and Ashley, 1984, 1990a, b, 1991, 1992, 1993a, b, Volcaniclastic rocks greatly predominate and compose what c, d; Evarts and others, 1987; Swanson, 1989, 1991, 1992, previous workers in the quadrangle have called the Ohana- 1993,1994a) into the now classic stratigraphic section in the pecosh Formation (Hammond, 1980; Swanson and Clayton, Mount Rainier-White Pass area defined by Fiske and others 1983; Winters, 1984; Stine, 1987; Korosec, 1987). Fluvial (1963; see also Waters, 1961) and modified by Vance and micaceous arkose and mudstone are interbedded and mixed others (1987). This work is establishing an improved re­ with the lower part of the volcaniclastic section (Winters, gional geologic framework for the southern Washington 1984; Swanson, 1994b). Many intrusions, mostly sill-like Cascades and defining a geologic research corridor across and generally basaltic andesite or andesite, cut the layered the west side of the Cascade Range (Swanson and Evarts, rocks. Pleistocene basalt, andesite, and dacite flows underlie 1992; Evarts and Swanson, 1994), from the upper Eocene much of the eastern part of the quadrangle. Most of the lava marine rocks of the Puget Lowland to the Late Jurassic- flows were erupted from vents east of the quadrangle, but Early Cretaceous Rimrock Lake inlier (Miller, 1989; Miller flows of andesite and dacite on Goat Ridge apparently have and others, 1993) along and just east of the crest in the White a local source. A subglacial volcano lies just east of the Pass-upper Tieton River area and eastward to the margin of quadrangle. the Columbia Plateau (Swanson, 1978) (fig. 1). The ongoing Glacial drift covers large areas, but generally bedrock study will provide geologic support for a seismic refraction crops out along creeks, steep slopes, and ridges. The bedrock and reflection study (conducted in late summer 1995) and mapping involved traverses along most drainages, large and other geophysical surveys in a corridor linking coastal Wash­ small; such work finds many exposures, even in densely ington with the Columbia Plateau (Wells and others, 1993). forested terrain. Detailed field work is testing whether a pronounced electri­ Previous small-scale (1:100,000 and smaller) reconnais­ cal conductivity layer in the middle crust, the southern sance geologic mapping has included the Hamilton Buttes Washington Cascades conductor (SWCC) of Stanley and quadrangle, mainly by Hammond (1980), Korosec (1987), others (1987, 1992), has a recognizable influence on the and Smith (1993).