Geological Survey Bulletin 1359 Geology and Mineral Resources of the Northern Part of the North Cascades National Park, Washington

This report was started as part of a study of the North Cascade Primitive Area, an area of about 830,000 acres, which adjoined the Canadian border on the north and which extended from Mount Shuksan on the west to Rock Mountain on the east. In the fall of 1968, Public Law 90—544, 90th Cong., reclassified the North Cascade Primitive Area and certain other national forest lands and created the North Cascades National Park, the Ross Lake National Recreation Area, and the Pasayten Wilderness. Ross Lake National Recreational Area, a corridor 2-1/2—4 miles wide along the Skagit River and its dammed portions, Ross, Diablo, and Gorge Lakes, separates the park into two parts and separates the northern part of the park from the Pasayten Wilderness.

The present study concerns those parts of North Cascades National Park and the Ross Lake National Recreation Area that are north of Skagit River and west of Ross Lake (fig. 1), as well as part of the Mount Baker National Forest west of the park (pl. 2).

LOCATION AND GEOGRAPHY

The northern part of the North Cascades National Park, Whatcom County, Wash., lies across the precipitous Picket Range and extends for about 22 miles along the Canadian border from Ross Lake on the east to Mount Shuksan on the west (fig. 1). The area covers approximately 500 square miles of steep mountains and densely forested valleys along the backbone of the Cascade Mountains. The highest peak is Mount Shuksan, whose ice-clad summit at 9,127 feet towers 7,000 feet above the broad forested Nooksack River valley to the north and 8,000 feet above the Baker River to the south. Other peaks, such as Glacier Peak, Mount Redoubt, Mount Challenger, Mount Fury, Luna Peak, Mount Terror, Crooked Thumb Peak, and Nooksack Tower, rise majestically above glacial-debris-filled cirques to elevations of more than 8,000 feet. Numerous small glaciers (fig. 2A, B) commonly occupy cirques along the higher ridges, especially on their north and east sides. Three glaciers, the Sulphide and East Nooksack glaciers on Mount Shuksan and the Challenger glacier on Mount Challenger, are more than 2 miles long and half a mile wide. Many small rivulets of melted water from the glaciers and snow banks coalesce into streams that cascade down the mountains in narrow V-shaped valleys or steep-walled chutes (fig. 16C). These streams join to form larger streams or rivers. The larger streams, such as the Chilliwack River, Little Beaver Creek, Big Beaver Creek, and the Baker River, occupy broad U-shaped valleys excavated by glaciers during the ice age. The upper parts of the ridges, above 5,500 feet, are generally bare of trees. The lower slopes and the valleys are densely forested with dark-green conifers, and parts of most stream bottoms have light-green tangles of vine maple, alder, and devilsclub.

FIGURE 1.—Location of the North Cascades National Park, which is divided into a northern part (1) and a southern part (3) by the Ross Lake National Recreation Area (2). The area covered by this report includes the northern part of the park (1) and that part of the recreation area (2) that is north of the Skagit River and west of Ross Lake. (click on image for an enlargement in a new window)

FIGURE 2.—Glaciers in the North Cascades National Park. A (top), Small glaciers that hug the steep north slopes of Easy Ridge. Pioneer Ridge in background. B (bottom), Glacier at head of Depot Creek cirque on the northeast Side of Mount Redoubt.

The climate is moderately cool and wet. Summer temperatures range from warm to cool; winter temperatures are cold. Precipitation ranges from about 70 to 110 inches a year, with a general increase from east to west. August is the driest month and generally the best time to visit the national park. Most of the precipitation comes as snow that in some of the higher areas accumulates to as much as 30 feet thick. Snow generally covers most of the area between mid-October and late May. Trails over some of the high passes, such as Hannegan and Whatcom Passes, may not be free of snow until mid-July.

Several roads approach the northern part of the park from the north, south, and west. Ross Lake, on the east border, may be reached from the north by 40 miles of secondary road from Hope, British Columbia, or from the south by 27 miles of road up the Skagit River from Marblemount, Wash. The latter road, which is part of the trans-state highway (Washington Highway 20), runs along the south shore of Ruby Arm of Ross Lake. The western part of the park may be approached from Canada by following a logging road up Slesse (Silesia) Creek to within 1 mile of the U.S. border. The most used approach is from the west, where 48 miles of paved highway from Bellingham, Wash., connects with 5 miles of dirt road up Ruth Creek to within 4 miles of Hannegan Pass. The west edge of the area may also be approached from Concrete, Wash., by 20 miles of dirt road past Baker Lake to its end on Baker River. Many of these roads lead to trails that provide the main access to the area. Trails up Baker River and Silesia Creek enter the western and northern edges of the national park. A main trail into the area goes from the end of the Ruth Creek road across Hannegan Pass and down the Chilliwack River. A branch of this trail crosses the Picket Range at Whatcom Pass and continues down Little Beaver Creek to Ross Lake. In the upper part of Little Beaver Creek, another branch of the trail follows Big Beaver Creek to the dam on Ross Lake. A detailed outline of trails and climbing routes in this area is given by Tabor and Crowder (1968).

PREVIOUS GEOLOGIC STUDIES

Geologic work in the northern part of the North Cascades National Park has been mainly of a reconnaissance nature. Daly (1912), between 1901 and 1906, made a reconnaissance map of a strip about 2 miles wide along the Canadian border. Misch (1952, 1966) studied parts of this area and published two geologic maps, at scales of 1:713,940 and 1:533,550, that include this area. More detailed work includes a thesis by Shidler (1965), who described the geology on either side of Silver Creek, and a description of the copper-molybdenum property on Silver Creek by Purdy (1954, p. 87-88). This and two other molybdenum properties in Sulphide basin were described by Moen (1969, p. 76-78).

PRESENT STUDIES

The present study began in 1965 as a mineral survey of the North Cascade Primitive Area. The mineral survey was undertaken in response to the Wilderness Act (Public Law 88—577, Sept. 3, 1964) and the Conference Report on Senate Bill 4, 88th Cong. and had as its objective an appraisal of the mineral potential of the primitive area. The work consisted chiefly of reconnaissance geologic mapping and extensive sampling. Sediment samples were taken along the major streams and most of the tributaries. Areas of altered or mineralized rock that were found were sampled, as were all known prospects and accessible mine workings. County courthouse records were searched for information on recorded claims, and a further search for these claims was made in the field.

Public Law 90—544, Oct. 2, 1968, 90th Cong., abolished the North Cascade Primitive Area and established the North Cascades National Park, Ross Lake Recreation Area, and Pasayten Wilderness. The part of the former primitive area lying east of Ross Lake was included in the Pasayten Wilderness. Our studies of the Pasayten Wilderness and certain adjacent lands and of the eastern part of the Ross Lake Recreation Area are described in another report (Staatz and others, 1971). The present report concerns the part of the former primitive area west of Ross Lake, most of which is now part of the North Cascades National Park.

The geology of the northern part of the North Cascades National Park is shown on plate 1, and the sample localities are shown on plate 2. The area is covered by planimetric and topographic maps on several different scales. Two topographic maps at a scale of 1:24,000 (Ross Dam, Diablo Dam) cover the southeast corner of the area; all or parts of four topographic maps at a scale of 1:62,500 (Mount Shuksan, Mount Challenger, Lake Shannon, Marblemount) cover the western two-thirds of the area. Most of the eastern part of the area is not covered by a large-scale topographic map. The whole area is covered, however, by all or parts of six U.S. Forest Service planimetric maps at a scale of 1:62,500. These maps were used for plotting our sample localities (pl. 2) and for field mapping. The only topographic map that covers the entire area is the U.S. Geological Survey Concrete sheet at a scale of 1:250,000 which was enlarged to a scale of 1:200,000 and used as a base for the geologic map (pl. 1).

ACKNOWLEDGMENTS

The daily use of a helicopter made possible extensive coverage of the area in a short time, and we owe much to the skill of two pilots, Robert Nokes and Emery Lamunyon. Fieldwork was carried out from late June to early September of 1966 and 1967. We were assisted in the field during the summer of 1966 by B. O. Culp, R. G. Smith, E. E. Loeb, and Russell Robinson, Jr., and during the summer of 1967 by E. E. Loeb, D. O. McKeever, J. H. Hanley, and J. W. Harbuck. During both summers C. L. Whittington operated a mobile geochemical laboratory in the field. He was assisted by W. H. Raymond, Jr., in 1966 and by E. K. Ragsdale in 1967. For a week during the summer of 1967, D. J. Grimes, R. T. Hopkins, and R. P. Hannan operated a mobile spectrographic laboratory at our base camp.

Samples collected by the U.S. Bureau of Mines were analyzed for gold and silver by the atomic absorption method by W. A. Barry in the laboratory of the Bureau of Mines, Reno, Nev. Copper, molybdenum, lead, and zinc analyses of these samples were made by colorimetric methods by Peter Mack of Wallace, Idaho.