Geological Survey Bulletin 611 Guidebook of the Western United States: Part A

SHEET No. 20. (click on image for an enlargement in a new window)

Beyond Thompson River the dip of the rocks brings the outcrop of the Newland limestone down from the tops of the hills (see fig. 31), but at this place it extends for only a mile or so and is cut off by a fault that trends about N. 20° W. and crosses the railway near milepost 29. As shown on the map, this fault separates the Newland limestone on the east from the Ravalli quartzite on the west.

On approaching Thompson Falls the traveler can see on his right a hill, and, if his eyesight is particularly good, he may be able to detect on its summit a steel tower erected by the United States Forest Service. On this tower during the summer is stationed an observer, who with powerful glasses watches for forest fires. As he can see on all sides for a distance of 50 miles, if the weather is clear, he is generally able to detect a fire soon after it starts and to notify the nearest ranger by telephone. Forest fires, especially such as swept through these mountains in 1910, not only burn a great amount of valuable timber but may also destroy towns along their pathway, with considerable loss of life. Under the present system of observers on high stations and an efficient organization for fighting fire, the destruction of timber has been greatly reduced and the loss of life nearly eliminated.

The town of Thompson Falls took its name from the falls of the same name, which were discovered in 1809 by David Thompson, the explorer and astronomer of the Northwest Fur Co. The water here falls 50 or 60 feet over resistant ledges of the Ravalli formation. It is estimated that with proper installation 40,000 horsepower could be generated at this fall. A dam is now being constructed, and electric power is to be furnished to the mountain division of the Chicago, Milwaukee & St. Paul Railway, 35 miles to the south. It is reported that any surplus power may be utilized in a similar manner by the Northern Pacific Railway.

West of Thompson Falls the bluffs on the right recede so far from the river that the rocks composing them are unrecognizable from the train, but the Ravalli formation¹ shows at railway level dipping toward the west, and across the river the Newland limestone is present in the tops of the hills. This formation appears to be flat, but that is because the traveler is looking at the edge of beds that dip directly away from him. This relation of limestone and quartzite to the river and railway holds in a general way from Thompson Falls to Noxon.

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¹The northern Rocky Mountains are made up largely and in some places wholly of the formations constituting the Belt series. These formations consist of sandstone, shale, and limestone, but the limestone is generally a small part of the entire mass. The sandstone is in many places changed to quartzite and the shale to argillite (a hard, slaty shale). These rocks were first studied in detail by C. D. Walcott in the Belt Mountains, east of Helena, Mont., and hence are known as the Belt series.

Very few fossils occur in the series, and those that have been found bear very little resemblance to the Cambrian faunas with which they should be most closely related. The only traces of animal life so far discovered in the sandstones and argillites are a few fragments of a small crustacean and the trails of worms. The limestones are crowded with peculiar coral like forms, which Walcott has recently determined to be fossil algae similar to the algae now growing in some of the lakes of New York. Walcott concludes from a study of the fossils mentioned that the large region in Montana, Idaho, and Alberta, Canada, underlain by the Belt series was during their deposition a continental area on which the sediments were deposited by rivers or in shallow lakes. The appearance of the rocks confirms this view, for all of them, even including many of the thick beds of limestone, are ripple marked, showing that they were deposited in shallow water. In places the argillite contains mud cracks and prints of raindrops, which could have been made only when the soft material was above water level and exposed to the drying effect of the atmosphere or the beating of the storm. By piecing together measurements made in several places, it is estimated that the Belt series, so far as it has been seen, is from 25,000 to 30,000 feet thick; but the base has not yet been found, and its real thickness may not be very much greater.

In this great mass of material certain parts, on account of their composition and association with other beds can readily be separated and identified in the areas in which they have been studied; but other parts have no characteristics by which they can readily be distinguished, and consequently different workers have classified them in different ways.

The two units most easily identified are the Newland limestone, which Walcott first recognized in the Belt Mountains, and the Helena limestone, which he named from its occurrence at the capital of the State. The general section along the Northern Pacific Railway, according to F. C. Calkins and J. T. Pardee, is as follows:

Formations composing the Belt series along the Northern Pacific Railway.

	Thickness in feet.
Helena: Limestone, dark blue or gray, weathering buff	2,400
Empire: Shale, greenish gray, or quartzite	600
Spokane: Shale or argillite, with some sandstone, all deep red	1,500
Greyson (Striped Peak): Shale, dark gray or green, with some white quartzite	3,000
Newland: Limestone, blue, thin bedded, but with some heavy bedded buff layers	2,200
Ravalli: Quartzite with some dark bluish or greenish shale	2,000
Prichard: Shale, dark bluish, interbedded with sandstone; base not exposed	8,000
	19,700

The rocks of the Belt series occur along the Northern Pacific Railway from the Bridger Mountains on the east to Sandpoint on the west. In the eastern part of this area they form the core of most of the mountain ranges, but west of Bonita they are the only hard rocks to be seen, with the exception of a few intrusive masses, to Pend Oreille Lake. They form the mountains of Glacier National Park and extend along the Rocky Mountains from the southern boundary of Montana, south of Butte, far into Canada, covering a territory about 500 miles long by 200 miles wide at the widest place.

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At Kildee, near milepost 37, the railway crosses the river, and from this point to Trout Creek there are two lines; the "high line" keeps up on the bench away from the river and the "low line" runs near the stream. The latter affords many interesting views of the river, which flows in a gorge cut a hundred feet or so in the floor of the old broad valley.

This part of the valley of Clark Fork was not seen by Lewis and Clark, but it was discovered soon afterward by the agents of the various fur companies, then exceedingly active in exploring new territory, and later it was examined in detail by the Government engineers.¹

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¹Soon after the return of Lewis and Clark the adventurous agents and explorers of the fur companies were engaged in examining every valley in the Northwest for fur-bearing animals and selecting sites for trading posts on almost every navigable stream and lake. Most of these advance guards of white civilization kept no record of their wanderings, but two of them, Alexander Henry and David Thompson, connected with the Northwest Fur Co., left excellent notes of their explorations and their dealings with the Indians in the northern United States and southern Canada in the early years of the nineteenth century. Alexander Henry was a fur trader with only one ambition, to further the interests of the Northwest Fur Co.; but David Thompson was an astronomer and scientific explorer, and his notes afforded much more accurate data regarding the character of the country and the location of important places than those of almost any other man who traversed this region in the early days. The territory covered by these men was largely the same, but Thompson explored the region about Clark Fork and Pend Oreille Lake, while Henry was engaged in trade with the Indians at the head of the Columbia.

In 1806 Thompson descended Kootenai River to about the place where the present Idaho-Montana line crossed that stream and proceeded southward along an old Indian trail across the Cabinet Mountains to Pend Oreille Lake. He reached the outlet of Clark Fork into Pend Oreille Lake September 9 and built a trading post on the point just north of it. This post he called Kullyspell House, from the name of an Indian tribe. In the modified form of Kalispell this name is now applied to a thriving town on the Great Northern Railway, near the north end of Flathead Lake. So far as known, this was the first visit of a white man to Pend Oreille Lake and Clark Fork. From Kullyspell House Thompson explored the valley down past Sandpoint as far as Priest Rapids and up Clark Fork and Flathead River to Dixon, where the Flathead reaches the railway from the north. On one of these trips up the river he established another trading post near the falls that were subsequently named in honor of their discoverer. This post he called Saleesh House, from the native name for the Flathead Indians. After the establishment of these trading posts Thompson continued westward to the Columbia, and he was the first white man to pass down that stream from the mouth of Priest River to Pasco, where the Northern Pacific Railway now crosses the river.

Although the fur traders explored the valley of Clark Fork as early as 1806, their reports were made only to the officials of the companies, who had no interest in promoting settlement, and consequently the public had little information concerning this interesting region until it was examined by the Government engineers who in 1853-54 explored it thoroughly to find the best route for a Pacific railroad. In 1853 Lieut. R. Saxton passed this way on his route from the Pacific coast to the headquarters of the expedition in the Bitterroot Valley. Saxton proceeded up Columbia River and across country to Pend Oreille Lake, which he reached August 12. He found that, owing to the high, steep mountains, it was impossible to pass around the south end of the lake, and he had considerable difficulty in skirting the north end, where Hope is now situated. He then proceeded up Clark Fork, but he found the route very rough and difficult, for the stream in many places swung so close to the bluffs as to make it necessary for the party to find a way over the rough mountain sides. After passing Thompson Falls and ascending Flathead River to the site of Dixon, he went up the Jocko and crossed the summit at the head of the Coriacan Defile to St. Mary (Stevensville), in Bitterroot Valley.

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The railway, from the point where it crosses Clark Fork to Trout Creek, follows the outcrop of the Ravalli formation, which dips to the left; and it is probable that the hills on the left are composed of the next higher formation, the Newland limestone, but they are so far distant and so nearly covered with trees that it is doubtful if the traveler will be able to distinguish formations.

Just beyond milepost 50 the train crosses Big Beaver Creek, a large stream joining the river from the south, and a little farther on Vermilion Creek enters from the other Side. The valley of the Vermilion is particularly interesting, for at its mouth there is a marked delta, visible from the train on the high line, which is 320 feet above the present river level. This delta could have been built only when the valley of Clark Fork was filled with water up to that altitude, and it probably marks some stage—possibly a closing stage—of glacial Lake Missoula. The reason why the valley of Vermilion Creek contains a more pronounced feature of this kind than the adjacent tributary valleys is that it connects at its head by a low pass with a valley draining into Kootenai River to the north. Through this low pass a large stream evidently flowed from the north at some time in the remote past. At that time all the Kootenai Valley, the next valley to the north, which is followed by the Great Northern Railway, was filled with an ice sheet that came down from the north, blocking all the previously existing water-courses and discharging at least part of its waters through the valley of Vermilion Creek. The sand and gravel carried by this stream were dumped into Lake Missoula when it stood 320 feet above the present level of Clark Fork. This was doubtless only a temporary outlet, else more material would have been brought down, possibly enough to completely fill the valley of Clark Fork.

At Trout Creek the hills on the south are composed of the Newland limestone, which dips toward the river at an angle of 40°. It is probable that this is the same belt of limestone as that which was seen on the left at a point just below Thompson Falls, and it is undoubtedly the same as the limestone which occurs on the south side of the valley as far as Noxon.

A short distance beyond Trout Creek the river makes a decided bend to the left and swings against the bluffs on that side. The railway follows the river and at milepost 59 is close to the mountain side, which is nearly bare, having been swept clean of trees in the great forest fires of 1910. On one of these smooth slopes horizontal beach lines are visible. They can be identified up the slopes to a height of 1,200 feet above the river, or 3,500 feet above sea level, but beyond that height no trace of such markings has been found. The uppermost beach line here probably corresponds with the highest one observed near Missoula and Dixon and, as these beach lines were formed by the same body of water and therefore must have been horizontal, it is almost certain that the crust of the earth has been tilted since the disappearance of the lake, the surface about Missoula having been raised 1,000 feet above that at Trout Creek, as explained on page 134.

Just beyond milepost 59 the roadway is cut in the base of a high cliff which is composed of Newland limestone lying nearly horizontal. The argillites and quartzites showing across the river and in the pyramidal island in the stream are vertical, hence there must be a fault between them which coincides in a general way with the course of the river.

Near milepost 67 a charming view is to be had of the cliffs on the south, which stand like a huge castle with battlemented walls.

The Newland limestone is exposed almost continuously along the river from milepost 59 to Noxon and for some miles beyond. It is generally horizontal or dips slightly to the northwest.

Nearly opposite milepost 74 Bull River joins Clark Fork from the north. This tributary valley is connected by a broad, deep trench directly through the Cabinet Mountains with the valley of Lake Creek, affording in glacial time a direct outlet for the great mass of ice that kept crowding down from the northern country. In this great trench the ice at its maximum was at least 2,000 feet deep. As soon as it emerged into the more open valley of Clark Fork it was reinforced by a large ice tongue that came down by Sandpoint and deployed up the Clark Fork valley. These two masses blended and filled the valley from Pend Oreille Lake to Noxon, forming an effective barrier across the pathway of the stream. Behind this barrier the body of water known as glacial Lake Missoula accumulated. In its passage up the valley the glacier left abundant evidence of its presence and work by the scouring which the valley received, the scratches on the rocks, and the bowlders of granite and other crystalline rocks which it carried into this area. The bowlders were not only dropped upon the valley floor, but many of them were left stranded on the valley wall up to a height of at least 2,000 feet above the stream.

Beyond Bull River there is little of interest for some distance. The valley walls are composed of Newland limestone, which dips gently downstream. Just beyond milepost 87, a few miles west of Heron, the train crosses the State line into Idaho, the boundary being indicated by a signboard.

To those who remember Idaho in their school geographies as a small pink block, shaped like an easy chair facing east, it may be of interest that this State, which in 1890 added the forty-fifth star to the constellation on the flag, is nearly as large as Pennsylvania and Ohio combined and larger than the six New England States with Maryland included for good measure. It is divided into 33 counties, the smallest of which is half as large as the State of Rhode Island and the largest exceeds the combined area of Massachusetts and Delaware.

Idaho covers an area of 83,888 square miles, divided principally between the Rocky Mountain region and the Columbia Plateau, only a small part, in the southeast corner of the State, lying in the Great Basin. In elevation above sea level the State ranges from 735 feet, at Lewiston, to 12,078 feet at the summit of Hyndman Peak. It is drained by the Columbia mainly through Snake River and its tributaries, and has an annual rainfall of about 17 inches, the range in a single year at different places being from 6 to 38 inches.

The industries of the State are chiefly agriculture, stock raising, and mining. Hay, wheat, oats, and potatoes are the principal crops.

A large area is cultivated by irrigation. The mineral production includes gold, silver, copper, lead, and zinc. The output of lead in 1913 was valued at $13,986,366, that of silver at $6,033,473.

The population of Idaho in 1910 was 325,924.

A short distance west of the Idaho line the Newland limestone, which has formed the walls of the valley for the last 10 or 12 miles, dips below water level, and the quartzites of the overlying formation (Striped Peak) appear. These rocks are so much harder than the limestone that the river has succeeded in cutting through them only a narrow, tortuous passageway known as Cabinet Gorge (Pl. XXI, p. 143). The river pours its whole volume through a crooked defile not over 100 feet wide, and it is estimated that 40,000 horsepower could be developed here with the natural flow of the stream. The gorge is soon passed, so that those who wish to see it should keep a close watch on the right as soon as they cross the State line. Beyond Cabinet station as far as milepost 91 there are many cuts in bright-red and green argillite and thin beds of sandstone (Striped Peak formation) overlying the Newland limestone. These mark the middle of a broad, flat syncline, which crosses the river in a north-south direction. Farther west the rocks dip upstream, and at the railway bridge the top of the Newland limestone may be seen on the north bank of the river.

PLATE XXI.—CABINET GORGE, IDAHO. Clark Fork here passes through a chasm which it has cut in red shale and sandstone (Striped Peak formation). The gorge at is narrowest part is about 100 feet wide. Rocks dip gently to the right. Photograph copyrighted by Haynes, St. Paul, Minn.

The village of Clark Fork is situated at the head of the delta which Clark Fork has built where it enters Pend Oreille Lake. Below the village the track winds about in the broad plain of the river bottom, skirting shallow bays and swamps and winding among rocky islands that rise here and there in the delta plain. The rocks are limestone (Newland), dipping up the stream toward the axis of the syncline, but about 2 miles from the village the whole of the limestone has risen above water level, and the underlying red argillites and quartzites (Ravalli) are exposed in the cuts.

West of milepost 97 the traveler may get glimpses here and there of Pend Oreille Lake, but it is not until the train approaches Hope that an unobstructed view may be obtained. If it is a clear day, the waters ripple in the sunshine against a dark background of rugged mountains, but if the air is hazy the lake seems to disappear in the distance between misty walls that rise on either side. One can but wonder what lies beyond that rocky gateway and long to board the little steamer lying at the dock and explore its remotest reaches. The broad expanse of water along the north shore is broken by several wooded, rocky islands that add greatly to the charm of the picture.

The French term pend (pendant) d'oreille means literally earring and was doubtless given to this lake by the early French explorers on account of its peculiar shape; but some authorities say that the name was originally given to a tribe of Indians because of their custom of wearing earrings and then was applied to the lake because these Indians inhabited its shores.

The lake is about 50 miles long and from 2 to 15 miles wide, and it is said to be very deep. As it is long and narrow and lies between mountains 2,000 to 3,000 feet high, it must, if the reported depth of water is correct, occupy a canyon rivaling in size and depth the Grand Canyon of the Colorado, in Arizona.

On the shore of the lake, near the place where Hope now stands, were once the main trails that led into the Kootenai country to the north. Over these trails supplies for the mining camps and goods for trade with the Indians were taken in and cargoes of precious furs brought out, but the traffic has ceased and the trails have become impassable. Hope is built on the side of a mountain so steep that its streets occupy levels 300 feet apart. It is important now as the site of a large sawmill and as a port for the small traffic on the lake.

The rocks back of Hope belong to the Prichard formation, which extends for about 7 miles, but they are cut by many dikes of granite similar to the great mass west of Sandpoint. The rocks also show greater metamorphism (changes due to pressure or to heat) toward this mass of granite, and on this account do not bear a close resemblance to those of the same age farther east.