mcpeaks
BLM
U.S. DEPARTMENT OF THE INTERIOR
BUREAU OF LAND MANAGEMENT
closeup2 Drill rig in the Powder River Basin, Wyoming. Livestock grazing in Wyoming. Pipeline construction in the Powder River Basin, Wyoming. Wyoming landscape.
Wyoming
BLM>Wyoming>Field Offices>Buffalo>Recreation>Petrified Tree
Print Page
Buffalo Field Office

Dry Creek Petrified Tree EEA Virtual Tour

Scoria is a sort of natural brick formed from shale or sandstone that has been "fired" when coal seams caught fire and burned back into the ground. Scoria can be crushed and used as a rock aggregate for road pavement, hence some of the red color roads in the area, and as a road base for unimproved roads. The red color is produced by iron oxides in the rock. Scoria can be crushed and used as a rock aggregate for road pavement; hence, some of the red-colored roads in the area, and as a road base for unimproved roads.

Coal forms slowly over great periods of time. The coal beds in the area originally accumulated as peat deposits that formed from the leaves, branches, stems, and roots of trees and other plants that grew in the swamps. The peat beds probably were buried when a nearby river flooded, covering the area with sand and mud. After millions of years under thousands of feet of sediment, the peat gradually changed to coal. (One coal seam near Buffalo, the Healey, is about 200 feet thick in places.)

As erosion and uplifting began to change the earth's surface, many coal seams were exposed to air and caught fire. As the coal seams burned back into the hillsides, the intense heat changes the normally soft brown and gray rocks to a hard red material--scoria. At station 2 you will learn about plants that helped to form the coal.