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The Geology of Mount Rainier National Park




No landmark is more familiar to the people of western Washington than the volcanic cone of Mount Rainier. Rising to a height of 14,408 feet it is the highest volcano in the United States, exclusive of Alaska, and towers 9,000 feet above its immediate base. The base, in this case, is the mile high Cascade Range which trends in a north-south direction dividing the State of Washington into two distinct units.

To the east is the Columbia plateau consisting of a tremendous series of basaltic flows collectively known as the Columbia River lavas. These also extend into eastern Oregon and southern Idaho and cover a total area of approximately 200,000 square miles. Continuing northward from the Columbia plateau are the Okanogan highlands composed of older plutonic and metamorphic rocks.

To the west of the Cascades is the Puget Sound depression which also trends in a north-south direction. The rocks in this trough are marine and brackish water sediments and intercalated volcanics, all of Tertiary age. Much of this area is covered with glacial deposits which locally may attain thicknesses of 1,000 feet. Farther to the west rise the northward extension of the Coast ranges in the prominent Olympic Mountains.

Mount Rainier is located on the top of the central Cascades, approximately 150 miles south of the Canadian border and 80 miles north of the Columbia River, the southern boundary of the State. To the north this range also bears the volcanic cones of Mount Baker and Glacier Peak; to the south are Mount St. Helens, Mount Adams, Mount Hood, and numerous others, extending down to Mount Shasta and Lassen Peak in northern California. In this chain, Lassen Peak, Crater Lake, and Mount Rainier are the only peaks which have been awarded National Park distinction.

FIG. 1. Mount Rainier from the west side of Pinnacle Peak.


Mount Rainier National Park is readily reached in a single day's journey, by auto, from the principal cities of the northwest. Routes of approach extend to all four corners of the Park. The Nisqually entrance, in the southwest corner, is joined to Tacoma and the Pacific Highway, some 56 miles to the northwest, by an excellent paved road. The Carbon River entrance and the Mowich entrance are located in the northwest corner and may be reached from Tacoma, 46 miles distant, or from Seattle, which lies 76 miles to the northwest. The Puget Sound approach to the White River entrance, or northeast corner, is made through Enumclaw, where paved roads leading from Tacoma, Seattle, and other Pacific Highway points converge. The eastern Washington approach to the White River entrance is made through the city of Yakima over the Naches Pass highway which crosses over the summit of the Cascades. In the southeast corner, the Ohanepecosh entrance is reached from Tacoma or from Mary's Corner on the Pacific Highway; the road then follows the Cowlitz River up to the Park.

FIG. 2. Index Map Showing the Location of Mount Rainier National Park.


While engaged as a ranger and ranger-naturalist in the National Park Service from the years 1929 to 1933 inclusive, the writer became interested in many of the geological problems in the Park. Actual field work was carried on during the months of September from 1930 to 1933 inclusive and again in 1935 a few weeks were spent in the field.


The writer wishes to express a sincere debt of gratitude to Professor G. E. Goodspeed of the University of Washington for his interest and aid in this work and for his many valuable suggestions.

It is a pleasure to acknowledge the many kindnesses shown by members of the National Park Service and especially Supt. O. A. Tomlinson, Chief Ranger John Davis and Park Naturalist C. F. Brockman.

Mr. Keith Whiting has aided the writer considerably in the field.


Spanish explorers entered what is now known as Puget Sound in 1790 and must have been familiar with Mount Rainier as seen from a distance, but so far as records go, they did not give a name to the mountain. (27)

Later, in 1792, Capt. George Vancouver explored and mapped a portion of Puget Sound and named many prominent features of the Sound and the adjacent territory. Mounts Baker, Hood, and Rainier were named at this time in honor of the officers of the British Admiralty. When Vancouver anchored near what is now Port Townsend, he (45) noted that,

A very remarkable, high, round mountain, covered with snow, apparently at the southern extremity of the distant range of snowy mountains (Cascades) before noticed, bore south 45° east.

When further south in Puget Sound, he (45) recorded:

The weather was serene and pleasant and the country continued to exhibit between us and the eastern snowy range the same luxuriant appearance. The round, snowy mountain now forming its southern extremity, and which, after my friend, Rear Admiral Rainier, I distinguish by the name of Mount Rainier, bore N. 42° east.

Probably the most vivid narrative in the history of Mount Rainier is the story of the first ascent, in 1870, by General Hazard Stevens, (35) who was accompanied by P. B. Van Trump. Their superstitious Indian guide, Sluiskin, led them as far as Paradise Valley and pleaded with them to go no further. Unheeding, the two men made the ascent by the Gibraltar route which, even today, is the most popular approach to the summit. After being forced to spend the night in the crater, they descended the following day by the same route. Sluiskin had given up all hope of these men ever returning and, as he was preparing to leave, Stevens and Van Trump walked into camp.

As the stories of these early visitors to Rainier began to spread, several mounaineering and scientific organizations became interested in the region and took active measures to encourage its adoption into the National Park System. Such men as John Muir of the Sierra Club, T. W. Powell of the American Association for the Advancement of Science, Bailey Willis of the United States Geological Survey, and G. G. Hubbard of the National Geographic Society, were extremely influential in having this area set aside as a National Park by an Act of Congress in 1892. The area of the Park, as originally defined, was 378 square miles, but 53 square miles were added when the eastern boundary was extended to the summit of the Cascades by an Act of Congress in 1931.


The earlier geological work in the vicinity of Rainier was practically confined to reconnaissance explorations carried on by the United States Geological Survey during the latter part of the nineteenth century. Emmons and Wilson of the 40th Parallel Corps, under Clarence King, made an ascent (8) of the mountain in August, 1870, and gathered geological data and specimens, but unfortunately, the records of their work are limited to a very brief publication, dealing chiefly with the glaciers.

Iddings, in 1833, made use of the data and the specimens collected by Emmons and collaborated with Hague (15) in preparing a paper on Mounts Hood, Shasta, Lassen, and Rainier. With the aid of chemical analyses and petrographic descriptions, they came to the conclusion that the lavas of these four cones were very similar and stated: "Mount Rainier is composed almost wholly of hypersthene andesite." In the same year, and under almost identical circumstances, Oebbeke (23) examined a specimen from Mount Rainier which had been collected by Professor Von Zittel. Oebbeke was particularly intrigued by the hypersthene and tried to isolate enough of the mineral for chemical analysis; this failing, he gave a fairly complete list of its optical properties.

In 1896, Russell (27) published a paper describing in detail each of the major glaciers and many of the smaller ones. His narrative includes a graphic account of a trip to the top of the mountain and an excellent description of the summit area. He also makes frequent statements concerning the general geology. A few of these are quoted on the following pages.

Mount Rainier is a typical example of a lofty volcanic cone built largely of projectiles, but containing also many lava streams. It belongs with the class of volcanic mountains known as composite cones. At one time the mountain was more lofty than it now is, its reduction in height being due to an explosive eruption which blew away the upper 2,000 feet of the original cone, leaving a great crater in the truncated remnant. After the loss of the summit, the mountain was not symmetrical; the rim of its great summit crater was the highest on the west, and lowest and probably breached on the eastern side. At a more recent date, two small craters were formed by mild explosive eruptions within the great crater and nearly filled it. The building of these secondary craters partially restored the symmetrical outline of the top of the mountain but gave to it a dome shape instead of a conical summit.

Smith (30) made a reconnaissance trip to the north and east sides of the mountain during the field seasons of 1895-96 and published an excellent eight-page summary of the various rocks encountered. He states:

Two classes of rock are to be discussed as occurring on Mt. Rainier; the lavas and pyroclastics, which compose the volcanic cone, and the granite rocks, forming the platform on which the volcano was built up.

These two papers by Russell and Smith are the most comprehensive works on the geology of the Rainier area.

In 1900, Smith (29) published a rather popular account of the geology of the Park in Mazama, a mountaineering journal of the northwest. In this he says: "The date of the uplift of the Cascades was not earlier than the close of Tertiary time." He also describes the building up of the cone and emphasizes the destructive power of the past and present glacial systems.

In 1905, Landes (19) published some "Field Notes on Mount Rainier," in which he describes the pre-Rainier topography and mentions a few localities where this surface was deeply eroded. Landes also calls attention to the composite nature of the cone and the effects of the glaciation. For the last 30 years practically no work of a geological nature has been done within the Park, with the exception of Matthes' masterly description of the glaciers. (21)


The cone of Mount Rainier, rising 14,408 feet above sea level, is so dominating a feature that the lesser portions of the topography seldom receive their due share of attention. For a better understanding of the Park as a whole, it seems wise to consider, first, the features of the Cascade Range independently of Mount Rainier.

The Park is located on the western side of the Cascades, extending from the main divide almost to the western margin of the range. This area can scarcely be regarded as a slope, as the peaks in the general upland surface maintain a remarkably constant elevation—approximating 6,000 feet—regardless of their position in the Park.

The sculpturing of the Cascades in this vicinity has been described as follows: (22)

To one standing on the flanks of Mount Rainier, the surrounding crests and ridges appear like the waves of a turbulent sea. Although infinitely diverse in sculpture, none conspicuously outtops its fellows and, at a distance, all seem to merge into one vast mountain platform.

This mountain platform has a very inconspicuous divide. On the eastern side, the rivers are roughly parallel and trend in a general southeasterly direction, finally emptying into the Columbia River. On the western side of the range, practically all the major rivers flow in a westerly direction and emerge upon the plains of Puget Sound.

These rivers, augmented by local glaciation near their sources, have bitten well over 3,000 feet into the Cascade upland. The valleys are noteworthy because of the low, flat bottoms, the remarkably steep sides, and the extremely low gradient they possess up to within a few miles of the main divide. Adding to this decided relief the upland surface is a maze of pinnacles, spires, knobs, and knife-like ridges which have been sharpened by small alpine glaciers. It is upon these rugged westward trending ridges and valleys that the cone of Mount Rainier is superimposed. Although the Cascades are more than a mile in height and have been deeply dissected, they dwindle to a rather indefinite base when compared to this volcano which towers 9,000 feet above them. This height is even more impressive when the mountain is viewed from any of the neighboring towns which are practically at sea level.

Although two peaks in the United States are higher, Mount Whitney, in California, and Mount Elbert, in Colorado, which top Rainier by 93 feet and 12 feet respectively, they rise but a few thousand feet from their immediate surroundings. On Rainier, the elevation changes from 2,000 feet to more than 14,000 feet within the short distance of 10 miles.

The volcano itself does not enjoy the dainty symmetry of Fujiyama but is, rather, a huge, broad-shouldered cone of somewhat irregular shape, being elongated, both at its summit and at its base in a northwest-southeast direction. Its rather bulky shape is perhaps more easily understood when one realizes that the flows from this 9,000-foot cone seldom spread more than 6 miles from the central vent.

Covering the top and streaming down the sides of the cone is the largest single peak glacial system in the United States, exclusive of Alaska. These tongues of ice, averaging between 4 and 6 miles in length, have carved out tremendous cirques and canyons in a radial fashion about the summit. The loosely consolidated rocks of the upper reaches of Rainier have allowed the glaciers to entrench themselves with comparative ease. However, the ice-scoured canyons are not limited to the slopes of the mountain but extend beyond and continue down into the older lavas and granodiorite below. The extreme ruggedness and scenic beauty of towering ridges and glacial canyons was undoubtedly the greatest factor in having this area preserved as a National Park.

Between the glaciers are lofty, vertical-walled slivers of rock which have been fashioned by ice into unusual shapes. Most picturesque are the triangular areas resembling the prow of a battleship cutting the swells, and, on the map, these forms are labelled "prows," "wedges," or "cleavers." For a vivid word picture and a complete description of all the glaciers, the reader is referred to the writings of Matthes and Russell. (21) (27)


A noteworthy feature of the topography is the superposition of the radial drainage pattern of Rainier upon a previous pattern in which the main rivers were essentially parallel and drained to the westward. Although the actual volcano of Mount Rainier occupies only one-fourth the area of the Park, the drainage pattern inherited from this mass completely dominates the entire Park and also influences the drainage for a considerable distance outside. However, as the cone is located on the western side of the range, all the major rivers are finally turned westward and reach the Pacific Ocean either through Puget Sound or, as in the case of the Cowlitz, through the Columbia River.

The Nisqually Puyallup Carbon, White, and Cowlitz rivers originate on the higher slopes as glaciers. At an elevation of approximately 4,000 feet, the glaciers terminate and the melting ice and snow above give rise to full-fledged streams which emerge from below the glaciers. The milky appearance of these streams is due to the particles of pulverized rock or "rock flour" suspended in the water.

Falling and cascading down deep canyons, the rivers lose their elevation rapidly and soon spread out, in a very leisurely fashion, on rather wide valleys which are but slightly elevated above sea level. The remainder of their westward course is over the softer sediments and glacial drift of Puget Sound. Occasionally interbedded flows or intrusives have provided more resistance to the cutting power of the rivers, and, in such cases, narrow canyons and gorges are formed locally. Examples are to be seen near the Carbon River bridge and in the La Grande Canyon of the Nisqually River; both are located outside and to the westward of the Park.

In a region of such high altitude, the melting snows contribute generously to the rivers, which during the spring months are enlarged to torrents. Most tables (16) show the discharge to reach its maximum during the month of June. All during the summer months the melting effect is very obvious. This is especially impressed on hikers going around the mountain on the famous Wonderland Trail. These people are obliged to cross all the radiating rivers at various times of the day. In the early morning, the streams and rivers are mere trickles to what they will be later in the day when the warm sun has had its effect on the glaciers and snow fields above. During the early evening the clunking of large boulders is a familiar noise as they are pushed along by the swollen streams.

Many factors exert a steadying influence on the rate of the run-off. The precipitation is not extremely variable although 90 per cent falls from October to May. This would diminish the run-off during the summer months, were it not for the aid given by melting snow.

The soils within the Park are almost strictly volcanic in origin, and, being quite porous, provide a good moisture retainer. This is aided by grass and flower growths which mat the ground at elevations between 4,000 and 5,000 feet. Below this level and down to 2,000 feet, the soil is a spongy mat of volcanic and vegetable debris which is highly absorbent. Held in place and aided by the thick underbrush and a dense forest growth, the conditions for water retention are ideal. Consequently, water and power sites are numerous. Already many of the larger cities of the Puget Sound region receive their power and water from this supply, but a great number of potential sites remain untouched.


The western side of the Cascades is well-watered by the moisture-laden winds coming in from the Pacific Ocean. This cooling mountain barrier causes the clouds to rise and expand with the resultant effect of precipitation.

In the Puget Sound depression the rainfall averages from 40 to 50 inches annually but, as one goes higher up the flanks of the Cascades, the increased cooling effects cause a gradual increase in the amount of precipitation. Snoqualmie Pass is one of the lowest points on the summit of the range and here the average total precipitation is 144 inches annually. As this location is 3,000 feet in elevation, a good portion of this falls as snow. Within the boundaries of the Park, the United States Weather Bureau (9) gives the following data: The Carbon River entrance at an elevation of 1,760 feet has a total precipitation of 91 inches annually; while at Longmire, which is 2,760 feet above the sea, it is 113 inches. At Paradise, a mile in elevation, no figures are given for the total precipitation, but the total snowfall is well over 500 inches annually. This corresponds closely to the total for the Snoqualmie Pass region.

Few places exist within the Park boundaries where the precipitation does not fall as snow at some time during the winter. This is in contrast to the very mild climate enjoyed in the Puget Sound area where snow, at any time during the year, is uncommon. Because the snow conditions are so ideal on the slopes of Rainier, this area has enjoyed widespread popularity as a site for skiing and allied winter sports. Thousands are attracted weekly during the winter and spring months to participate in these sports. At the settlement of Paradise, the first snows usually fall in October, and all during the winter and early spring months the ground is covered to a depth of 10 to 15 feet. The drifts linger well into July. However, at Longmire, the time and amount of snowfall is most irregular and, no matter how severe the winter has been, with the coming of May, all the snow is melted.

During the relatively short summer season the climatic conditions are nearly perfect. The crispness of the mountain air, the warm sunshine, and cool, clear nights unite with the scenery to attract hundreds of thousands of people annually to this national playground.


In a region with such a wide range of altitude, the environmental conditions for plant and animal life are extremely varied. As a result, Taylor and Shaw (36) have been able to divide the Park into zones corresponding to those established by Dr. H. C. Merriam. Each of these zones is based largely on latitude but, as a change in altitude on a high mountain has a very similar effect to a change in latitude, many zones can be represented on a single peak. In a general way, the contour lines define the zones but these are often obscured by the powerful influence of moisture. The four zones—the Arctic Alpine, the Hudsonian, the Canadian, and the Transition are represented within the Park. Of all the zones in the United States only the Sonoran is missing.

The Transition zone, between the Sonoran and Canadian, is the smallest and least important in the Park. It is characterized by the grand or white fir, salal, Oregon grape, vine maple, devil's club, and salmonberry. Typical animals include the California quail, Seattle wren, Oregon ruffled grouse and chickadee, as well as the mink and racoon.

The Canadian zone, from 4,500-5,000 feet in elevation, is a heavily-timbered area containing Douglas fir and western hemlock of huge diameter and height. Other members of the flora include lovely fir, noble fir, lodgepole pine, mountain ash, forest anemone, and alpine beauty. Among the fauna are the Cooper chipmunk, snowshoe rabbit, Stellar jay, and the western pileated woodpecker.

Between the elevations of 4,500-6,500 feet, or in the Hudsonian zone, are the flowers for which the Park is famous. The rather dense woods in the lower portion of this zone gradually dwindle until they meet the open grassy parks or the jagged glaciated peaks. Alpine fir, mountain hemlock and Alaska cedar are the dominant trees. The heathers (Phyllodoce and Cassiope), avalanche lily, gentian, huckleberry, squaw grass, and lupine are only a few of the hundreds of species of flowers found in these natural garden spots. The chipmunk, mantled ground squirrel, cony, and marmot are all familiar sights to the Park visitor.

Above the 6,500-foot contour, 80 square miles of the mountain belong to the Arctic-Alpine zone. Sharing this region with the glaciers are the mountain goat, ptarmigan, Hepburn rosy finch, and the pallid horned lark. Such flowers as the golden aster, Indian paint brush, yellow heather, Tolmie saxifrage, and pigeon-billed lousewort exist on these high slopes. No mention of the fauna should exclude black bear, that trouble-making clown of all the animals, who ranges from the lower Park boundaries to timberline.

The Department of the Interior has issued a series of pamphlets on glaciers, (21) birds and mammals, (36) forests, (1) and flora (10) of the Park which contain detailed and specific information on these subjects.

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Last Updated: 28-Mar-2006