Mr. Arnold Hague gives the following graphic account of this and adjacent areas:

From one end to the other the Absarokas present a high, imposing plateau, with elevations ranging from 10,000 to over 12,000 feet above sea level. The entire mass is made up almost exclusively of Tertiary igneous rocks. *** Degradation of the mass has taken place on a grand scale. Vast quantities of volcanic ejectmenta have been removed from the summit, but no reliable data exist by which the amount can be estimated even approximately. All the higher portions have been sculptured by glacial ice. Enormous amphitheaters have been carved out of the loose agglomerates, and peaks, pinnacles, and relics of great table-lands testify in some measure to the forces of erosion. The plateau is scored by a complete network of deep valleys and gorges, which dissect it in every direction, and lay bare the structure of the vast volcanic pile.[1]

Within the park there is evidence of similar volcanic activity, and it is clear that the basin between the encircling ranges was filled to its present elevation by volcanic flows, which formed the present park plateau. The area within which the fossil forests are now found was apparently in the beginning an irregular but relatively flat basin, on the floor of which after a time there grew the first forest. Then there came from some of the volcanoes, probably those to the north, an outpouring of ashes, mud flows, and other material which entirely buried the forest, but so gradually that the trees were simply submerged by the incoming material, few of them being prostrated. On the raised floor of the basin, after a time, the next forest came into existence, only to be in turn engulfed as the first had been, and so on through the period represented by the 2,000 feet or more of similar beds. The series of entombed forests affords a means of making at least a rough estimate of the time required for the upbuilding of what is now Specimen Ridge and its extensions. (See p. 27.)

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.