The Eocene Green River Formation underlies an area of about 15,000 sq mi in Colorado, Utah, and Wyoming. It consists principally of organic marlstone (oil shale), marlstone, siltstone, sandstone, and intercalated tuff beds that were deposited in fresh-water, saline-lacustrine, and associated deltaic and fluviatile environments.

The tremendous shale-oil potential of the formation is well known; oil shale that yields an average of 15 gals of oil per ton may contain about 2 trillion bbl of oil, or oil shale that yields an average of 25 gals of oil per ton may contain more than 750 billion bbl of oil. In Utah, gilsonite veins are associated with the Green River Formation, and oil and gas have been found in the shore facies. Recent discoveries, however, have shown that saline minerals are an important part of the economic potential of the formation.

The soda-ash industry in Wyoming, which mines the large deposits of bedded trona in the Green River Formation, is expanding rapidly. In the Piceance basin of Colorado, recent core holes have shown that nahcolite (NaHCO₃) is locally abundant, and that dawsonite (NaAl[OH]₂CO₃) a potential source of alumina, is disseminated in rich oil shale in significant amounts.

The discovery of large quantities of saline minerals suggests that in future exploration the Green River Formation should be considered as a multiple mineral resource. Because of the fine-grained nature of the rocks, discovery of other potentially valuable disseminated minerals like dawsonite will require advanced research tools such as X-ray diffraction and X-ray fluorescence for rapid quantitative analysis of numerous samples. With the use of such tools, the prospects seem bright for finding new mineral resources, for the major part of the Green River Formation is still virtually unexplored.

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