Proceedings of the California Academy of Sciences, Volume III, 1863-1867

by Various

Origin of the Submerged Forests in the Columbia River, Oregon.

BY WM. P. BLAKE.

The submerged forests of fir trees, extending about twenty-five miles along the Columbia River, above the Cascades, have long excited the curiosity of travelers upon that stream. The trees stand erect as they grew, but the tops have decayed and broken off, leaving only those portions of the trees that have been protected from the air by the covering of water. At extreme high-water very few of these old trunks can be seen, but at low-water they appear in great numbers, and project a few inches or feet above the surface, and in some places they extend far out into the stream.

These trees are not petrified, as is supposed by many. The outer portions are much softened and partly decayed, but towards the heart the wood is sound, and appears to be identical in character with the fir which covers the mountains around. Some cedar stumps are also found.

It is well known that fir trees will not grow below the high-water mark of our streams, or where the roots would be subject to overflows. Flooding the roots of the fir even for a few days is sufficient to destroy its life. It is thus clear that there has been a change in the level of the water since the forests grew. Either the land has sunk or the water has been raised: the latter appears to have been the fact.

The river at the Cascades, just below the submerged forests, plunges over great masses of a hard volcanic conglomerate, which forms the base of the cliffs on each side. This conglomerate, which is 150 to 200 feet thick, rests upon a stratum of sandy clay. This stratum is much softer than the conglomerate, and yields more rapidly to the action of running water. It may be seen when the water is low, at the foot of the Cascades, with the hard conglomerate overhanging it in large masses.

From all these facts, it appears that the river, in cutting its way downwards through the Cascade Range, reached this soft substratum, and for a long time flowed in a comparatively unobstructed channel at a much lower level than now, thus permitting the forests to grow along its banks. The extensive undermining of the conglomerate caused it at length to fall into the stream, and this, together with the sliding in of the banks upon this soft foundation, I regard as forming the obstruction which dammed the waters and caused the overflow of the forests above.

The mountains rise on each side to a height of 2,500 or 3,000 feet, and are composed of nearly horizontal beds of lava. One of these mountains on the right bank, or Washington Territory side, presents vertical cliffs towards the Cascades, and these cliffs have a freshly broken appearance, as if a large part of the mountain had broken off at no very remote period. The surface of the country between this cliff and the Cascades is very much broken, and the railroad which traverses it, exposes enormous masses of the conglomerate, piled confusedly together as if they had been hurled down by a land-slide. Mr. Brazee, the engineer of the Oregon Steam Navigation Company, informs me that the ground is in constant motion toward the river, and it has necessitated the relaying of the track within the past year. The same phenomena have been observed on the left bank, or Oregon side. The bank is in constant motion there, and at low-water a fine blue clay may be seen rising in the channel, as if crowded out by the pressure of the rocks above. As there has not been any perceptible change of level in the stream for years past, we may conclude that the erosive action of the current is fully equal to the encroachment of the banks.

The Indians of the Columbia have a tradition of a great convulsion at the Cascades. They assert that the Chinook canoes formerly ascended the river as far as a water-fall at the Dalles, passing, at the Cascades, under a bridge of rock. This bridge, or arch of rock, they say, fell in at the time of a quarrel between the two mountains, Mt. Hood and St. Helen’s, and at the same time the waterfall at the Dalles was destroyed, so that salmon could ascend to the Upper Columbia. Before that the fall was so high that salmon could not get up, and all the upper country Indians were obliged to go to the Dalles for their supply.

The general accuracy of this tradition seems highly probable. The Dalles are now a succession of rapids and low falls, in a narrow channel, between vertical walls of basaltic lava. There is very little fall or current in the river below the Dalles to the Cascades, and the elevation of the water by an obstruction at the latter point would in all probability affect the height of the lower fall at the Dalles.