During the time this 2,000 feet of material was being accumulated, and since then to the present day, there has been relatively little warping of the earth’s crust at this point; that is, the beds were then, and still are, practically horizontal, so that the fossil forests, as they are being gradually uncovered, still stand upright.
When the volcanic activities had finally ceased, the ever-working disintegrating forces of nature began to tear and wear down this accumulated material, eroding the beds on a grand scale. Deep canyons and gulches have been trenched, and vast quantities of the softer materials have been carried away by the streams and again deposited on lower levels or transported to great and unknown distances.
As the material in which the fossil forests are now entombed consist of ashes, mud flows, breccia, and the like, not all the beds are of the same texture end hardness, so that erosion has acted unevenly on them and has produced many peculiar rock forms. The grotesque so-called “hoodoos” have been carved out in this manner. The fossil trunks, being usually harder than the surrounding matrix in which they are embedded, have more firmly resisted erosion and now project to different heights above the general level. In exposed beds that are nearly or quite horizontal, disintegration has acted at nearly equal pace on the trunks and on the matrix, so that the trunks are nearly or quite on a level with the surrounding surface. On steep hillsides, however, from which all loose material is easily and quickly removed, some of the fossil trunks stand up to a height of 20 or 30 feet. If the beds had been tilted at a considerable angle, these trunks could project from the surface for only a short distance before their weight would break them off, showing again the remarkably stable conditions that have continued since the trunks were covered up.
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.[2]