U.S. DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP I–2538 U.S. GEOLOGICAL SURVEY GEOLOGIC MAP OF THE SNOQUALMIE PASS 30 × 60 MINUTE QUADRANGLE, WASHINGTON By R.W. Tabor, V.A. Frizzell, Jr., D.B. Booth, and R.B. Waitt INTRODUCTION mostly coincident with the Helena-Haystack mélange, is recognized in the Manastash Ridge area in the GEOLOGIC OVERVIEW southwest corner of the quadrangle. Tabor (1987) and Tabor and others (1989, p. 13) discuss the possibil- The Cascade Range of Washington State, a western ity that the Darrington-Devils Mountain Fault Zone rampart of the North American Cordillera, comprises has been the most recently active structure, locally an older basement of accreted terranes and a cover following the Straight Creek trend, but in fact trun- of sedimentary and volcanic rocks. The Snoqualmie cating the earlier structure. We will continue to re- Pass quadrangle (fig. 1, on map sheet) lies at the north fer to the north-south zone of faulting as the Straight edge of the volcanic cover, where the regional structural Creek Fault Zone (leaving out the and(or) Darrington- uplift to the north elevated the older rocks to erosional Devils Mountain Fault Zone). levels. Most of the quadrangle is underlain by Ter- Near the southeast corner of the quadrangle, the tiary rocks, but mélanges of Paleozoic and Mesozoic Straight Creek Fault Zone intersects the Olympic- rocks are exposed in structural highs in the northern Wallowa Lineament of Raisz (1945; see also Kienle part of the quadrangle. and others, 1977; Tabor and Frizzell, 1979) in a complex North of the quadrangle, the north-trending Straight of curving faults and folds. The Olympic-Wallowa Creek Fault cuts the mosaic of accreted terranes and mostly lineament, as originally defined, is expressed physi- separates higher grade metamorphic rocks of the North ographically from the Wallowa Mountains in Oregon Cascade crystalline core to the east from lower grade to the Strait of Juan de Fuca between the Olympic and unmetamorphosed rocks to the west. Rocks west Peninsula and Vancouver Island (see for example, Pike of the fault are further partitioned by a Late Cretaceous and Thelin, 1989). The lineament traverses the Sno- and (or) Paleogene suture (the Helena-Haystack mélange) qualmie Pass quadrangle almost diagonally from the and coincident Paleogene, high-angle Darrington-Devils southeast to northwest (fig. 1) and is expressed by Mountain Fault Zone. Rocks north and east of the suture a broad zone of faults and folds in rocks ranging in are in the Northwest Cascade System of Misch (1966), age from Jurassic to Miocene. The lineament is most as modified by Tabor and others (1989). Rocks in the strongly expressed in the faulted and folded rocks of suture zone itself comprise the Helena-Haystack mélange the Manastash River Block (fig. 2, on map sheet; Tabor of Tabor and others (1988, 1989; also Tabor, 1994), and and others, 1984, fig. 2) where the lineament meets rocks southwest of the suture form the western and eastern the Straight Creek Fault Zone. mélange belts (Frizzell and others, 1987; Tabor and others, Faults in the Straight Creek Fault Zone appear 1993). These latter named three fundamental western to swing southeastward into the lineament trend* (Tabor terranes are represented sparingly in the Snoqualmie Pass and Frizzell, 1979). The lineament loses definition quadrangle. where it crosses the Cascade Crest just west of the The Straight Creek Fault, and its probable exten- the Straight Creek Fault, but it appears to be expressed sions in Canada and Alaska (Price and others, 1985, in broad northwest-trending folds and faults in Mi- p. 3-48, 3-49), is a major strike-slip fault with post- ocene volcanic rocks between the South Fork of the mid-Cretaceous to pre-middle Eocene(?) right-lateral Snoqualmie and White Rivers. The nature of the deep- displacement variously estimated between 180 and 90 seated structure or structures producing the lineament km (Misch, 1977; Frizzell, 1979; Vance and Miller, is uncertain. It may contain elements of structures of 1981). The zone of faulting, representing the prob- different ages, including the Darrington-Devils Moun- able southward extension of the Straight Creek Fault tain Fault Zone. exposed in the Snoqualmie Pass quadrangle, has possibly also been the locus of strike-slip faulting in *Recent Mapping and stratigraphic revisions by Eric Cheney the Darrington-Devils Mountain Fault Zone, which (Cheney, 1999; see also Cheney, 2000) in the vicinity of Easton suggest that the Straight Creek Fault continues more or less straight south intersects the Straight Creek Fault at an acute angle from the northern part of Lake Kachess. The interested reader may (fig. 1). The Darrington-Devils Mountain Fault Zone, want to evaluate this new work. 1 Pre-arc rocks of the North Cascades to the north volcanic arc was well established; it flooded the Cascade of the Snoqualmie Pass quadrangle are offset right Range with calk-alkaline volcanic rocks, the princi- laterally across the Straight Creek Fault and, in the pal rocks exposed in the Snoqualmie Pass quadrangle. quadrangle terranes of the Northwest Cascade Sys- tem, crop out east of the fault. During the early to early middle Eocene, when the HISTORY OF GEOLOGIC MAPPING Straight Creek Fault and the Darrington-Devils Mountain AND ACKNOWLEDGMENTS Fault Zone were most active, regional extensional and transtensional faulting dominated the Pacific North- Geologic work in the Snoqualmie Pass 1:100,000 west (Tabor and others, 1984; Johnson, 1985; Heller quadrangle began before the turn of the century with and others, 1987; Tabor, 1994). The faulting promoted investigations of coal found along the Green River the formation of local basins wherein fluvial feldspathic (Willis, 1886, p. 759-760). The basic geologic frame- sediments and subordinate volcanic materials accumu- work east of the Cascade Crest was established by lated. By the middle Oligocene, movement on the major Smith and Calkins (1906) in the Snoqualmie Pass 30- structures had waned and the north-trending Cascade minute quadrangle, and subsequently many workers 20 North 6 5 14 Bend So uth 3 F 11 ork R Snoqualmie er S Pass 8 Riv n oqu Cedar almie 16 14 10 12 Kachess 4 8 Lake Keechelus 1 Lake Cle Elum Howard Stampede Lake Hanson Pass Reservoir Yakima Gr een Easton River Enumclaw River 13 Wh 19 13 ite 9 7 Greenwater F 17 N k 12 12 Lit R tle i v R Naches N e iv a r e Pass c 7 r h es 18 Creek R ow A 15 Cr 2 0 5 10 15 20 MILES 0 10 20 KILOMETERS 1. Ashleman, 1979 6. Erickson, 1969 12. Hammond, 1963 17. McCulla, 1986 2. Cambell, Newell (written 7. Fischer, 1970 13. Hammond, 1980 18. Smith, Gary (written commun., 1986) 8. Foster, 1960, 1967 14. Hammond, P.E. (written commun., 1986) 3. Chitwood, 1976 9. Goetsch, 1978 commun., 1977) 19. Stout, 1964 4. Clayton, 1973 10. Gower and Wanek, 1963 15. Hartman, 1973 20. Vine, 1962, 1969 5. Ellis, 1959 11. Gualtieri and others, 1975 16. Lofgren, 1974 Figure 3. Sources (keyed to map by number) of map compilation data for Snoqualmie Pass 1:100,000 sheet. A (1-20), for area 10 and 20 much data used with little to modest modifications. All other areas, some data used. Figure 3 con- tinued on next page. 2 (see fig. 3) have drawn on their ideas. Fuller (1925) Our work, begun in 1975, is part of a larger project was one of the first to address the complexities of that includes mapping the Wenatchee 2° quadrangle what we call the western mélange belt and to develop at 1:100,000 scale (Tabor and others, 1982b, 1987a, the idea that some of the bodies of magma that ul- 1993). Frizzell, Tabor, and Booth, with the ongoing timately formed the Tertiary batholiths vented to form assistance of Kathleen Ort, compiled and mapped most the Tertiary volcanic cover rocks, a theme since ex- of the bedrock geology. Booth mapped the unconsoli- panded upon (Cater, 1960, 1969; Fiske and others, dated deposits in the northwestern third of the map 1963; Tabor and Crowder, 1969). Hammond (1963) area and Waitt mapped unconsolidated deposits else- was the first to attack the difficult problems of re- where in the quadrangle. gional correlation presented by post-Eocene volcanic Our field work was considerably aided by the ef- rocks, and he has continued his regional studies in forts of Sharon Allshouse and Eduardo Rodriquez in subsequent years (Hammond, 1977, 1980). Detailed 1975, Jay Coburn and Ron Tal in 1976, Bill Gaum, mapping in the western foothills was begun on modern Margaret Goddard, and Kim Marcus in 1977, Eliza- base maps by Vine (1962) and Gower and Wanek beth L. Mathieson and Nora Shew in 1978, Steve (1963). Connally, Stephen A. Sandberg, Fred Beall, Frederika North 45 30 Bend Sou 22 th 24 34 F 26 ork R 39 S Snoqualmie 33 n Pass er oqualmie Riv 27 Ceda 42 r 37 Keechelus Lake Kachess 25 Lake Stampede Cle Elum Howard Pass Lake Hanson Reservoir Yakima 36 43 G reen 28 Easton River 21 Enumclaw River 44 41 W 29 hi & te 32 38 29 23 Greenwater N F 35 k Lit R tle i v R Naches N e iv a r e Pass c r h es Creek R 31 ow B 40 Cr 0 5 10 15 20 MILES 0 10 20 KILOMETERS 21. Beikman and others, 1961 28. Kinnison and Sceva, 1963 34. Mogk, 1978 40. Smith and Calkins, 1906 22. Bethel, 1951 29. Koesters, 1984 35. Newcomb, 1970 41. Treat, 1987 23. Crandell, 1973 30. Kremer, 1959 36.