The development during the past few years of commercial volumes of petroleum and natural gas in the Wasatch formation of northwest Colorado and southwest Wyoming has aroused considerable geological comment.

The Wasatch formation is of Eocene age and fluvio-terrestrial in origin. Geological field studies have established Wasatch sedimentation as of the continental type and definitely non-marine.

Petroleum and natural gas have been developed in and are now being produced from the Hiawatha member of the lower Wasatch. The production is believed to be indigenous to the Wasatch formation and not migratory from other formations. The occurrence of hydrocarbons in large volumes in a non-marine formation, and apparently indigenous thereto, is most unusual geologically.

The commercial accumulation of both petroleum and natural gas in the Wasatch formation appears to be controlled, in the main, by structural folding. However, the extreme lenticularity of the Wasatch sands and the resulant stratigraphic traps formed by sand lensing are of more importance locally than structural position in determining successful well locations. Over 25 separate gas productive lenses and five separate oil-productive lenses of variable sizes and shapes are already known to occur in the Hiawatha member of the Wasatch formation.

Four fields, namely, East Hiawatha, West Hiawatha, Powder Wash, and Canyon Creek have found commercial volumes of natural gas in Wasatch sand lenses. Two of them, East Hiawatha and Powder Wash, are productive of commercial quantities of petroleum, as well as natural gas, from the same Wasatch formation.

The economical development of petroleum and natural gas fields in the lenticular and somewhat erratic sands of the continental Wasatch formation involves production problems and hazards not common to the more regular sand-reservoir fields.

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