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Geologic map of the North Cascade Range, Washington

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Geologic Map of the Mount Baker 30'- by 60' Quadrangle, Washington
U.S. Geological Survey Investigation Series I-2660

by R.W. Tabor, R.A. Haugerud, W. Hildreth, and E.H. Brown

Prepared in cooperation with the Washington State Department of Natural Resources, Division of Geology and Earth Resources, Olympia, Washington, 98504

Generalized geologic map of the Mount Baker Quadrangle.
Click here for enlarged version with explanation (76K).

Thumnail view of generalized 
              geologic map of the Mount Baker Quadrangle
INTRODUCTION

The Mount Baker 30- by 60-minute quadrangle encompasses rocks and structures that represent the essence of the geology of the North Cascade Range . The quadrangle is mostly rugged and remote and includes much of the North Cascade National Park and several dedicated wilderness areas managed by the U.S. Forest Service. Geologic exploration has been slow and difficult. In 1858 George Gibbs (1874) ascended the Skagit River part way to begin the geographic and geologic exploration of the North Cascades. In 1901, Reginald Daly (1912) surveyed the 49th parallel along the Canadian side of the border, and George Smith and Frank Calkins (1904) surveyed the United States' side. Daly's exhaustive report was the first attempt to synthesize what has become an extremely complicated geologic story.

Modern geologic work began almost a half a century later when, in 1948, Peter Misch began his intensive study of the North Cascade Range (Misch, 1952, 1966, and see other references). His insights set the stage for all later work in the North Cascades. Considerable progress in understanding the North Cascades in light of modern plate tectonic theory has been made by E.H. Brown and his students. We have used much of their detailed geologic mapping. Although our tectonic reference frame has changed much with the recognition of plate tectonics and exotic terranes, Misch's observations prove to be remarkably accurate.

Our work in the Mount Baker quadrangle began in 1983 as part of a project to map and compile the geology of the Wenatchee and Concrete 1 X 2 degree quadrangles at 1:100,000 scale, work that we began in 1975. We have mapped in cooperation with the Division of Geology and Earth Resources, Washington Department of Natural Resources. We have also benefited by the cooperation and helpfulness of the National Park Service and the U.S. Forest Service.

The Problem of Names

Previous workers, including the present authors, have applied four kinds of names to geologic units in the map area, lithologic, time-stratigraphic, structural, and stratigraphic-structural (terranes) (TABLE 1). The plethora of terms is confusing to everyone, but the complexity of the geology allows little simplification. Much of the crust in northwest Washington appears to be built of accreted terranes, hence many units have been given terrane names in the past (cf. Tabor and others 1987a,b, 1989; Brandon 1989). On this map, even though most pre-Tertiary units are terranes or probable terranes, where possible, we have used established lithologic or time-stratigraphic names. In discussion, we commonly move up the nomenclatural ladder to a more comprehensive terrane name. Within the main text describing each unit or group of units, we discuss the use of the appropriate names. Names used in the General Geology overview, derive from the more lengthy discussion in I-2660.

 

Table 1. Nomenclature of terrane and structural elements in the Northwest Cascade System

Misch, 1966

Tabor and others, 1989

Brandon, 1989

This map

     

Gold Run Pass Nappe made up of parts of lower nappes

     

Gold Run Pass thrust

Shuksan thrust plate: composed of the Shuksan Suite of Misch (1966) made up of the Shuksan Greenschist and Darrington Phyllite

Easton terrane: composed of the Easton Metamorphic Suite made up of the Shuksan Greenschist and Darrington Phyllite

Easton terrane: composed of the Easton Metamorphic Suite

Shuksan Nappe: composed of Easton terrane made up of Easton Metamorphic Suite

Shuksan thrust

   

Shuksan Thrust

Imbricate zone:

included the Yellow Aster Complex of Misch (1966) and other highly faulted rocks.

Elbow Lake terrane

Yellow Aster terrane

Deadman Bay and related terranes: including the Elbow Lake Formation of Brown and others (1987)

Welker Peak Nappe: composed of the Bell Pass Melange which is made of the Elbow Lake Formation of Brown and others (1987) and Yellow Aster Complex of Misch (1966), and other units

Shuksan thrust

   

Welker Peak Thrust

Church Mountain thrust plate: composed of the Cultus Formation and Chilliwack Group of Cairnes (1944) [in which Misch (1966) included rocks now referred to the Elbow Lake Formation of Brown and others, 1987)]

Grandy Ridge terrane: composed of the Cultus Formation of Brown and others (1987), Chilliwack Group of Cairnes (1944), Nooksack Group of Danner (1958), and Wells Creek Volcanics of Misch (1966)

Chilliwack terrane and overlying clastic sequence: includes the Nooksack Group of Danner (1958), and Wells Creek Volcanics of Misch (1966), Cultus Formation of Brown and others (1987), Chilliwack Group of Cairnes (1944), as well as the Yellow Aster Complex of Misch (1966)

Excelsior Nappe: composed of the Cultus Formation of Brown and others (1987) and Chilliwack Group of Cairnes (1944)

Church Mountain thrust

   

Excelsior Thrust

Autocthon: composed of the Nooksack Group of Danner (1958), and Wells Creek Volcanics of Misch (1966)

   

Nooksack Formation

       

Acknowledgments

Many people have helped with field work in the difficult terrain of the Mount Baker quadrangle: Michael Ort (1984 1985), Patrick Goldstrand (1985), Carolyn Ortenburger (1985 1986), Janet Slate and Robert Fillmore (1986), Kathleen Duggan (1987 1988), Scott Spees (1987), Eric Roth (1988), Kris Alvarez (1990 1991), Tom Grundy (1990), Carmello Ferlito, David Maher and Jim Montgomery (1991), Chad Nelsen, Cathryn Dwyre, and Rob Osborn (1992). Hildreth began investigating the Quaternary volcanic rocks in 1992; for field assistance he is grateful to Kari Cooper, Mike Dean, Judy Fierstein, Ellen Lougee, Dave Tucker, and Patricia Weston. Many employees of North Cascades National Park and the Mount Baker Ranger District of the U.S. Forest Service have been helpful, in particular Craig Holmquist, Kevin Kennedy, Jerry Lee, and Bill Lester; Jon Reidel has been particularly helpful. We are thankful that superb helicopter pilots and their crews exist; thank you Tony and Sue Reese for our success and our safety.

We have discussed the geology of the map area with many. In particular we have enjoyed extended and sometimes heated discussions with Derek Booth, Mark Brandon, Darrel Cowan, Joe Dragovich, Bob Miller, the late Peter Misch, Jim Monger, John Reidel, John Stacy, Jeff Tepper, and Joe Vance. Darrel Cowan, Derek Booth, and Bob Miller made many helpful suggestions for improvement of map and text.

R.W. Tabor produced the Mount Baker digital geologic map with GIS technology using Alacarte (Wentworth and Fitzgibbon, 1991). Many computer and(or) GIS experts helped, especially Tracey Felger, Todd Fitzgibbon, Patricia Helton, Eric Lehmer, Bob Mark, Chad Nelson, Geoff Phelps, and Pahdy McCarthy. Many thanks to Carl Wentworth, who, no matter how busy, always answered questions about Alacarte.

Generalized geologic map of the Mount Baker Quadrangle.
Click here for enlarged version with explanation (76K).

Thumnail view of generalized geologic map of the Mount Baker Quadrangle

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