The Tower Sandstone at Green River is represented by lenses and channel fillings at several stratigraphic levels in the lower part of the Laney Shale Member of the Green River Formation (Eocene). The detrital fraction of the sandstone is composed of approximately 40 percent quartz, 25 percent feldspar, 6 percent biotite, 2 percent hornblende, and 25 percent lithic fragments; approximately 50 percent of this detrital material is of volcanic origin. Most of the volcanic material, along with varying amounts of grains or other origin, was reworked and redeposited by streams. Soon after burial, the sand and silt detritus was well cemented by calcite and iron carbonate. The cement comprises approximately 25 percent of the rock.