The Rocky Mountain region offers every type of structural and stratigraphic trap favorable for the accumulation of oil. The presence of many well defined surface anticlines has given the impression that this region is strictly a structural province and the stratigraphic trap has been relegated to a place of minor consideration.

Because of the profitable development of the Cretaceous sand traps along the east side of the Powder River basin of Wyoming, this type of accumulation will be elaborated on to indicate that where similar geologic conditions exist in other of the Rocky Mountain basins the same type of production can be expected.

Fundamental in this concept of sand trap accumulation is that structural considerations as we know them, do not apply. To discuss the various theories on the origin, migration and accumulation of oil to account for this type of accumulation is to beg the question. The fact has to be recognized that the Cretaceous sands of the Rocky Mountain region are extremely lenticular and are capable of forming favorable traps for the accumulation of oil due to the lensing of the sand members themselves--on structure, on regional dip, and in synclines.

To date no method, other than the drill, has been devised to isolate an oil-bearing sand lens with any degree of certainty that one will be found. This "punch-board" type of exploration and development drilling is frowned upon as being unscientific, but it has proved very profitable to many operators in the Powder River basin of Wyoming. From the economic standpoint it has several

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advantages in that very little preliminary geological work is required; because geophysics are of no aid in this problem they do not have to be considered; drilling depths can be chosen to suit the operator's equipment and finances; and finally, considerable latitude is offered in choosing a well site. Since there is no relationship between depth to the sand (if present) and production, the cost of exploring a sand lens area with wells 2,000 feet in depth (or less) would be commensurate to a core drill program of similar depth.

To support the contention that accumulation of the type discussed is more dependent on reservoir media than on structural considerations the following producing areas are cited.

1. Shannon pool off north plunge of Salt Creek, and Bothwell syncline west of Salt Creek field
2. Dakota production in Big Muddy field
3. Dakota production in East Lance Creek field
4. Dakota production in North Ant Hills area
5. Newcastle sand, Dakota and Lakota production in Mule Creek field
6. Dakota production in Bridge Creek area
7. Muddy or Newcastle sand production in Mush Creek-Newcastle-Osage fields
8. Dakota production in Lodgepole area
9. Frontier production in Upton-Thornton area
10. Newcastle sand production in Moorecroft area

All of the examples are in the Powder River basin of Wyoming.

In conclusion it should be mentioned that there are many other areas in the Rocky Mountain region where production of the type discussed can be obtained. It can be further stated that in any one of the Rocky Mountain basins where Cretaceous rocks are present the possibilities for sand trap accumulation exist.

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