YELLOWSTONE Fossil Forests of the Yellowstone National Park

The fossil forest that was first brought to scientific attention is on the northern slope of Amethyst Mountain, opposite the mouth of Soda Butte Creek, 12 miles southeast of Camp Roosevelt. The following account, by Dr. William H. Holmes, the discoverer of these fossil forests, shows the impression first made by them:

As we ride up the trail that meanders the smooth river bottom [Lamar River] we have but to turn our attention to the cliffs on the right hand to discover a multitude of the bleached trunks of the ancient forests. In the steeper middle portion of the mountain face, rows of upright trunks stand out on the ledges like the columns of a ruined temple. On the more gentle slopes farther down, but where it is still too steep to support vegetation, save a few pines, the petrified trunks fairly cover the surface, and were at first supposed by us to be shattered remains of a recent forest.¹

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¹Holmes, W. H., Twelfth Ann. Rept. U. S. Geol. and Geogr. Surv. Terr., 1878 (1883), p. 48.

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These trunks may easily be seen from the road along the Lamar River, about a mile away. They stand upright—as Holmes has said, like the pillars of some ruined temple—and a closer view shows that there is a succession of these forests, one above another. In the foothills and several hundred feet above the valley there is a perpendicular wall of volcanic breccia, which in some places attains a height of nearly 100 feet. The fossil trunks may be seen in this wall in many places, all of them standing upright, in the position in which they grew. Some of these trunks, which are 2 to 4 feet in diameter and 20 to 40 feet high, are so far weathered out of the rock as to appear just ready to fall; others are only slightly exposed; niches mark the places from which others have already fallen; and the foot of the cliff is piled high with fragments of various sizes.

Above this cliff fossil trunks appear in great numbers and in regular succession. As they are all perfectly silicified, they are more resistant than the surrounding matrix and consequently stand above it. Most of them are only a few inches above the surface, but occasionally one rises as high as 5 or 6 feet. The largest trunk observed in the park is found in this locality. It is a little over 10 feet in diameter, a measurement that includes a part of the bark. It is very much broken down, especially in the interior, probably having been so disintegrated before it was fossilized. It projects about 6 feet above the surface.

At many places about Amethyst Mountain there are numerous fragments of fossil wood and many hollow trunks. The material in which they had been embedded has been eroded away, and they lie around in somewhat the same attitudes that are shown by all the trunks in the Arizona fossil forests, but there is little doubt that they were originally erect and have simply fallen by their own weight because of the removal of the material around them.

Many of the trunks here, as well as elsewhere in the park, had decayed in the center before they were fossilized, and some of the hollow interiors are filled with clusters and rosettes of beautiful crystals of amethyst, which doubtless suggested the name given to the adjacent mountain. Much of this finely preserved wood, as well as the trunks containing the crystals of amethyst, was broken up and carried away by collectors of minerals and curiosities before the Government control in the park was made sufficiently rigid to insure proper protection.

In many respects the most remarkable of the fossil forests is on the northwest end of Specimen Ridge, about a mile southeast of Junction Butte and about opposite the mouth of Slough Creek. So far as known, this forest was first brought to scientific attention by Mr. E. C. Alderson, of Bozeman, Mont., and the writer, who discovered it in August, 1887. It is found on the higher part of the ridge, and covers several acres. The trees are exposed at various heights on the very steep hillsides, and one remarkable feature of the forest is that most of them project well above the surface.

One of the largest and best preserved trees stands at the very summit of the slope (see title page). This trunk, which is that of a giant redwood, is 26-1/2 feet in circumference without the bark and about 12 feet in height. The portion of this huge trunk preserved is the base, and it exhibits to a considerable degree the swelling or buttressing so well known in the living redwood. The roots, which are as large as the trunks of ordinary trees, are now embedded in solid rock.

On the steep hillside a short distance below the big tree just mentioned are the two trunks shown in figure 5. They are about 2 feet in diameter and 25 feet high, and stand some 20 feet apart, and we may imagine them to have formed the doorposts of the "ancient temple" of which Holmes speaks. Both these trunks are without the bark. On the left of the figure is one of the huge irregular masses of rock that has been carved out by erosion.

FIG. 5.—UPRIGHT TRUNKS IN SPECIMEN RIDGE FOSSIL FOREST.

In figure 6 is shown another trunk about 3 feet in diameter and nearly 30 feet high. In several places along the trunk the thick bark may be noted. This tree is a pine, as are the two last described, and slightly below and behind it are two living pine trees, which are about the size it must have been when living. Another trunk, some 12 feet in height, is shown in figure 7, and in figure 8 there may be noted a standing trunk and above it another that has recently fallen.

FIG. 6.—TRUNK OF FOSSIL PINE SHOWING BARK, SPECIMEN RIDGE FOSSIL FOREST.

FIG. 7.—TRUNK SHOWING BARK, SPECIMEN RIDGE FOSSIL FOREST.

FIG. 8.—UPRIGHT AND PROSTRATE TRUNKS, SPECIMEN RIDGE FOSSIL FOREST.

The height attained by the trees of this fossil forest can not be ascertained with certainty, since the tallest trunk now standing is only about 30 feet high, but every one observed is obviously broken off, and does not show even the presence of limbs. Perhaps the nearest approach to a measure of the height is afforded by a trunk (shown in fig. 10) that happened to have been prostrated before fossilization. This trunk, which is 4 feet in diameter, is exposed for a length of about 40 feet, and as it shows no apparent diminution in size within this distance it is safe to assume that the tree could hardly have been less than 100 feet high and very probably may have been higher. This trunk is wonderfully preserved. As may be seen from the illustration, it has broken up by splitting along the grain of the wood into great numbers of little pieces, which closely resemble pieces of "kindling wood" split from a clear-grained block. In fact, at a distance of a few yards it would be impossible to distinguish this fossil "kindling wood" from that split from a living tree.

FIG. 10.—PROSTRATE TRUNK OF FOSSIL REDWOOD, SPECIMEN RIDGE FOSSIL FOREST.

The large redwood trunk already mentioned (title-page) as being nearly 10 feet in diameter may be compared with its living relative of the Pacific coast in order to calculate its probable height. The living redwood is usually 10 to 15 feet in diameter and ranges in height from 200 to 340 feet, and as the two are so very closely related there is no reason to suppose that the fossil trunk was of less height, but by a moderate estimate it may be accredited with a minimum height of 200 feet.

The most accessible fossil forest, marked "Petrified Trees" on the map is west of the Tower Falls Ranger Station and Camp Roosevelt on the road from the Grand Canyon to Mammoth Hot Springs, by way of Mount Washburn. It is on the middle slope of a hill that rises about 1,000 feet above the little valley and may be reached by a branch road from the main loop road. As the traveler approaches the forest he will observe a number of trunks standing upright among the stumps and trunks of living trees, and so much resembling them that a near view is necessary to convince him that they are really fossil trunks. Only two rise to a considerable height above the surface. The larger one is about 15 feet high and 13 feet in circumference (fig. 11); the other is a little smaller. As the roots are not exposed, it is impossible to determine the position of the part in view or the original diameter of the trees, as the bark is nowhere preserved.

FIG. 11.—FOSSIL TRUNK NEAR TOWER FALLS. Photograph by F. J. Haynes.

Above these standing trunks lie many others, which the disintegrating forces of nature break up into small fragments and keep at about the same level as that of their surrounding matrix. Some of these trunks rise only a few inches from the surface; others are nearly covered by shifting debris. Their diameter ranges from 1 to 4 feet, and they are so perfectly preserved that the rings of growth can easily be counted. The internal structure is also in most trunks nearly as perfect as when the trees were living.

The forest that is next in size to the one a mile southeast of Junction Butte is on Cache Creek, about 7 miles above its mouth. It is on the south bank of the creek and covers several acres. The trunks are scattered from bottom to top of the slopes through a height of probably 800 feet. Most of the trunks are upright, but only a few project more than 2 or 3 feet above the surface. The largest one observed was 6 feet in height and 4 feet in diameter. Most of these trunks appear to the naked eye to be conifers, but a number are obviously dicotyledons—that is, they were deciduous-leaved trees. The conifers, however, were the predominant element in this as in the other fossil forests.

The slopes of the Thunderer, the mountain so prominently in view from Soda Butte on the south, also bear numerous fossil trunks. Most of them are upright, but only a very few project more than 2 feet above the surface. No remarkably large trunks were observed at this locality, the average diameter being perhaps less than 2 feet.

Mount Norris, which is hardly to be separated from the Thunderer, also bears a small fossil forest. The trees are of about the same size and character as those in the larger mountain. Fossil forests of greater or less extent, composed mainly of upright trunks, are exposed also on Baronett Peak, Bison Peak, Abiathar Peak, Crescent Hill, and Miller Creek. In fact, there is hardly a square mile of the area of the northeastern portion of the park that is without its fossil forest, scattered trunks, or erratic fragments.

The vast area east of the Yellowstone Lake and the region still farther east, beyond the limits of the park, have not been thoroughly explored, but enough is known to make it certain that these areas contain more or less fossil wood. The stream beds in these areas in many places contain fragments of fossil wood, which indicates that trunks of trees must be near at hand.