About 420 million bbl of oil has been produced from Salt Creek field, Natrona County, Wyoming. Most production is from the second Frontier sandstone, which is one of many sandstone bodies interbedded with marine shale in the lower part of the Upper Cretaceous in the Rocky Mountain area. The stratigraphic interval between the Mowry Shale and the Niobrara Formation contains the Frontier and equivalent formations. The interval containing this section is more than 1,000 ft thick in central, northeastern, and west-central Wyoming and in southeastern Montana. Another area of thick sediments within this interval is in northwestern Montana and western Alberta. In some areas this section is entirely marine shale; in other areas it contains numerous sandstone bodies. The sand was t ansported by a series of river systems that formed deltaic complexes or lobate sand concentrations at several places along the margins of the early Late Cretaceous sea. These deltaic deposits are represented by the "D" sandstone of the Denver basin, the Ferron Sandstone Member of the Mancos Shale of Utah, the Cardium and Bad Heart Sandstones of Canada, and the Frontier Formation of Wyoming.

The second Frontier sandstone--producing formation at Salt Creek field--is an offshore bar associated with the eastern terminus of one stage of Frontier deposition. The sandstone body is several miles wide, more than 60 mi long, and as much as 100 ft thick. Salt Creek anticline (formed in late Late Cretaceous or early Tertiary time) is in an area of excellent sandstone development where stratigraphic traps developed in which oil accumulated before secondary migration into present structural positions took place.

There are other sandstone bodies included in the Frontier depositional complex which contain stratigraphically trapped oil, but these are not draped over an obvious anticline. The Wind River and Big Horn basins, and parts of the Green River and Powder River basins, probably contain more "Salt Creeks"!