Geological Survey Bulletin 614 Guidebook of the Western United States: Part D. The Shasta Route and Coast Line

SHEET No. 6 (click on image for an enlargement in a new window)

From Yoncalla Valley (see sheet 6, p. 46) grain fields, orchards, and flowered pastures sweep up the gentle hillsides. Many of the hills in this vicinity are composed of Eocene sediments, but some may have been carved from basaltic lavas. The rocks to be seen on the long ascent to Rice Hill are largely shale and sandstone, but include a small mass of basalt. At the summit early in June are golden fields of St. John's wort (Hypericum), locally called goat weed.

Half a mile north of Oakland the railroad crosses Calapooya Creek, just beyond which, on the left, is a small lens of impure limestone of Eocene age that contains great numbers of fossils. To the right, beyond the station, can be had a view of Tyee Mountain, a part of the Coast Range. This range is more even crested here than it is farther north. Turning to the left the railroad goes through a sandstone ridge, near which are some tile works, and comes out on the flat valley called Camas Swale, where the thriving town of Sutherlin has recently sprung up. Camas Swale was once occupied by Calapooya Creek, but long before man had any knowledge of the region the creek deserted this valley for it's present course, north of Oakland, rejoining the old channel just below Stephens. Man has since compelled part of the water of the creek to return to the old valley, where it is used for irrigating numerous thrifty orchards and productive fields. To the west may be seen the Coast Range and, nearer at hand, the entrance to the crooked canyon through which Umpqua River runs northward to the mouth of Elk Creek, west of Drain, before turning to the sea. South of Camas Swale, to the left (east) of the track, are prominent hills of Eocene sandstone. Near Wilbur the sandstone is accompanied by masses of a rather coarse grained basaltic rock called diabase. This rock is believed to have been forced in a molten condition through the sand that was later consolidated into the Eocene sandstone while that material was being deposited on the sea bottom and to have been in turn covered by more sand. During the period of eruption deposit's of tuff, made up of fragments of the diabase, were also formed. This tuff contains fossils of the same kinds that are found in the sandstone. As Wilbur is approached some of the sandstone may he seen overlying the diabase and forming prominent bluffs on the left side.

Beyond Wilbur the railroad crosses some Eocene sandstone and then enters an area of diabase which extends to Winchester. Here North Umpqua River is crossed. To the left is a mill dam, a place of fascinating interest during the salmon season, when the big fish endeavor to jump over the dam instead of going up the fish ladder. Between Winchester and Roseburg the railroad crosses two areas of Eocene sandstone, but these are entirely surrounded by diabase, which continues to be the prevalent rock along the route as far as Green, 30 miles from Winchester.

A mile north of Roseburg the railroad reaches South Umpqua River, which unites with the North Umpqua to form the main stream in Garden Valley, a few miles to the northwest. At the left are bluffs of lava in which are inclosed some fragments of Eocene shale, as shown in Plate XIII (p. 35). Deer Creek is crossed just north of the town.

PLATE XIII.—SHALE INCLOSED IN DIABASE NEAR ROSEBURG, OREG. The diabase, an igneous rock, has broken up through the shale.

From Roseburg, which is the seat of Douglas County, a stage line runs across the Coast Range to Myrtle Point and Coos Bay. This bay is one of the important harbors of the west coast and the port of shipment for the Coos Bay coal which more coal than other field, produces any field in Oregon.

The bold hills about Roseburg are all composed of diabase. About 15 miles northeast of the town, on Little River, a tributary of the North Umpqua, above Glide, Eocene fossils are abundant.

A mile south of Roseburg the deeply decomposed diabase affords good examples of spheroidal weathering. Specimens were collected here for the educational series of rocks prepared by the United States Geological Survey and distributed in 1898 to all the higher educational institutions of the country.

At Green there is a sudden change to the older rocks that compose the Klamath Mountains—conglomerates, sandstones, and shales of Cretaceous age, associated with more siliceous rocks, hard sandstones, and cherts of Jurassic age, and slates, limestones, and greenish lavas of Devonian and Carboniferous age.

The core of the Klamath Mountains is composed of large masses of granitic rocks and serpentine, which are intruded into the Devonian, Carboniferous, and Jurassic rocks just mentioned. These older sedimentary rocks cross the country traversed by the railroad between Roseburg and Medford, occurring in belts running northeastward toward the Blue Mountains.

The hills at Green are smooth and rounded and for the most without trees. The rocks of which they are composed are of Mesozoic age, mainly sandstones and shales, with some conglomerate. These rocks are greatly crushed along a belt running northeastward. Southwest of Green station they are associated with a schist composed largely of the beautiful blue mineral glaucophane. This mineral, which is a rather rare variety of hornblende, is found in only a few parts of the world outside of Oregon, Washington, and California. With the glaucophane schist near Green occur a greenish mica schist, some flintlike rocks commonly called cherts, and a greenish igneous rock, referred to as greenstone, which has been so much altered that its original character is in doubt. The best exposure of the blue schist is three-fourths of a mile southwest of some farm buildings on the right (west) at milepost 567.

This is the only area near the Shasta Route in which these crystalline schists occur. On the other hand, the sandstones and shales with which the schists are associated occupy a large area that is traversed between Green and Dole, a distance of about 13 miles.

At Carnes, nearly 1-1/2 miles beyond Green, there is a view to the left up Roberts Creek to Dodson Mountain, a prominent peak standing 3,235 feet above sea level. In the distance are some outcrops of a limestone which is used for lime and cement.

At milepost 565 the South Umpqua is reached again by the railroad, which follows its right (east) bank. Along the stream the crushed sandstones and shales are well exposed to view.

Between Dillard and Dole the river cuts through a ridge, thereby making many fine exposures of the sandstones and shales. Fossils have been found at many places in the belt of rocks just traversed, but opinions differ as to whether the rocks are all Cretaceous or in part Jurassic.

From Dole (Ruckels post office) may be seen ahead, on the left, two ridges—one wooded, the other bare. The absence of trees on the second ridge is due to the fact that it is composed of serpentine, a rock containing much magnesia and yielding an unfertile soil. Serpentine is an altered form of certain igneous rocks that are as a rule dark and heavy and contain more magnesia and iron than ordinary igneous rocks. Their characteristic mineral is olivine or peridot, and on this account they are called peridotites.

At milepost 553 the serpentine, which forms a belt more than a mile in width, is visible close at hand. At milepost 551.4 it is cut by dikes of porphyry, an igneous rock containing crystals that are noticeably larger and more distinct than those which make up most of the rock.

A small cut at milepost 551 shows some fine conglomerate and sandstone lying at the base of a large mass of Lower Cretaceous sedimentary rocks (the Myrtle formation), over which the railroad runs for nearly 10 miles.

About 12 miles northeast of Myrtle Creek station, up the creek, considerable gold has been obtained by washing the gravels (placer mining), chiefly the gravels that overlie the igneous rocks of the region. Beyond Myrtle Creek the railroad crosses South Umpqua River and runs for some miles along the western border of the Missouri Bottom, where many kinds of fruits and grains are grown. On the right (west) is a prominent ridge of Cretaceous sandstone and conglomerate (Myrtle formation). These beds lap up over the serpentine of the ridge beyond.

At Riddle, in Cow Creek valley, the rocks contain many Cretaceous fossils, both plants and marine animals, and among the hills to the southwest, on Thompson Creek, there are also beds containing large numbers of Jurassic fossil plants.

Farther down the valley, among grain fields and prune orchards, may be seen on the right (northwest) a prominent, thinly wooded mountain of serpentine, in which there is a deposit of green silicate of nickel (garnierite). This mineral is extensively mined for nickel in the island of New Caledonia, east of Australia, but the Oregon deposit has not yet been successfully worked.

The distant bare hills seen to the right near the head of the valley are composed of serpentine, but the bluffs nearer at hand, on both sides of the track, consist of Eocene sedimentary rocks. Beyond these is the entrance to Cow Creek canyon, which has been cut through the serpentine belt of Nickel Mountain. The serpentine areas can generally be recognized from a distance by their greenish color and barren aspect. In places, however, they are covered with wild azalea bushes, which suggested the name Azalea for the now abandoned post office at the mouth of Doe Creek.

Between Iron Mountain (milepost 533) and Nichols shales and sandstones are exposed along Cow Creek and have yielded large collections of fossil leaves of Jurassic age, as noted below by F. H. Knowlton.¹ Many of these leaves belong to various species of ginkgo, or maidenhair tree, so called because its leaves resemble in shape those of the maidenhair fern. The ginkgo no longer grows wild on this continent, but it has been introduced from Japan and is common m many of our cities. The rocks in which these leaves are found belong to a formation not yet finally named.

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¹The flora of the Jurassic period is in many ways one of the most remarkable fossil floras known. Although not large—it contains probably less than 200 known species—it is practically world-wide in distribution, ranging from King Karl's Land (82° N.) on the north to Graham Land (62° S.) on the south, and has been found in nearly every country on the globe. It is especially abundant in the western hemisphere, occurring in Spitzbergen, King Karl's and Franz Josef lands, Greenland, Siberia, Alaska, and abundantly in Oregon and California.

The luxuriant vegetation and magnificent forests of western and southern Oregon give so impressive an air of permanence and solidity that it seems as if the conditions now found there must have been unchanged from the beginning of time, yet we have but to turn to the study of the vegetation entombed in the wayside rocks to prove conclusively that during Jurassic time the land was clothed with a flora totally unlike that which now covers it. In the Jurassic period, whose antiquity can be measured only in millions of years, the dominant types of vegetation were ferns and cycads, which were accompanied by smaller numbers of conifers, horsetails, and the curious ginkgo. The types dominant in the flora of to-day are the monocotyledons (grasses, sedges, lilies, palms, etc.) and the still more abundant dicotyledons (oaks, elms, maples, etc.), but so far as we know no plants belonging to either of these great groups existed in Jurassic time.

A few miles southwest of Riddle there has been found a flora of about 70 species, making this one of the richest localities in the world for plants of Jurassic age. Of these species about 20 are ferns, 30 are cycads, and 10 are conifers, and the remainder belong to a number of more or less doubtful groups.

The largest number of ferns belong to the extinct genus Cladophlebis, mainly rather small ferns with much-divided fronds. Another wholly extinct form is Taeniopteris, which has long, narrow fronds similar in type to the grass fern, now found in this country only in Florida. Adiantites is believed to be one of the ancestors of the maidenhair ferns, of which there are many living species. There are also three that are thought to belong to living genera—Dicksonia, which is not now found in this country; Polypodium, which is now a very large, mainly tropical group, though a few small species are found in temperate lands; and Thyrsopteris, a fern with finely divided fronds, the only living representative of which is a species in the island of Juan Fernandez.

The cycads were not only the most abundant as regards different kinds but in individuals as well, some collections containing literally hundreds of specimens. They all belong to extinct tpes, and many of them were evidently large plants, probably with thick stems or possibly with trunks, at the top of which grew large compound leaves disposed in a circle or crown.

One of the most abundant and conspicuous plants of this flora was the ginkgo, of which four or five species have been found here. The ginkgo is now represented by a single species in China and Japan, where it is a more or less sacred tree, found about the temples. It is not certainly known to exist in a truly wild state anywhere. This tree has had perhaps a more wonderful history than any other now living. It appeared at least as early as the close of the great Paleozoic era, and by or even before the Mesozoic era it had waxed mighty and had spread over most of the world except the extreme southern hemisphere. It has come down to us so little changed that some of the leaves from the Jurassic rocks of Oregon, apart from their fossil character, are distinguished with difficulty from those of the living tree. (See fig. 8.) Had it not been for the fostering care of man the genus would apparently have become extinct several centuries ago.

FIGURE 8.—Sketch of a ginkgo leaf from the Jurassic beds of Oregon.

Associated with the ginkgo leaves in many of the Jurassic deposits of Oregon are a few branchlets of strange conifers, such as Sphenolepidium, Pagiophyllum, and Brachyphyllum; also a few forms that are referred with more or less uncertainty to living genera, such as Pinus (pine), Sequoia (redwood), Araucaria and Taxites (yew).

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From Nichols station a backward view may be had of the great flat top of Table Mountain, which is made up of horizontal Eocene strata. Cow Creek Canyon near Nichols has a depth of about 1,000 feet and is well wooded, though in a few places the woods are marred by fire. The most abundant trees are firs, to which the madronas, with their red-brown bark and shiny oval leaves, afford a pleasing contrast.

South of Nichols station the fossiliferous Eocene, Cretaceous, and Jurassic strata are succeeded by a very thick series of sandstones and shales, which form the slopes of Cow Creek canyon for nearly 15 miles. No fossils have been found in them in this area. This great mass of sandstones and shales (the Dothan formation, of Jurassic age) is much crushed, so that the layering characteristic of rocks that have been deposited in water has been obscured.

From West Fork mail is carried over a trail to the lower Rogue River country and to Gold Beach, on the coast. About 3 miles south of West Fork a large slide occurred some years ago on the west slope of the canyon and blocked railroad traffic completely for three months. Four miles of track had to be changed and two new tunnels cut.

At a number of places along this part of Cow Creek old stream gravels, lying on hillside benches above the channel of the present creek, have been worked for gold.

About 4 miles beyond West Fork the sandstones and shales of the Dothan formation are succeeded by a much more variable set of rocks, chiefly slates and greenstones. The slates are known as the Galice formation, from the mining district of that name in the Klamath Mountains, farther south. They contain fossils which are similar to those collected from the slates (Mariposa slate) of the gold region of the Sierra Nevada, in California, and which indicate Jurassic age. The Galice formation is older than the Dothan formation and ought normally to lie beneath it, but earth movements since the beds were deposited have reversed these positions and the Galice at this locality now lies on top of the Dothan. Such an overturn is sometimes brought about by folding of the beds, sometimes by faulting whereby older beds are slid on top of the younger ones.