The Wamsutter arch is a poorly defined, low-order, positive structural element of southwestern Wyoming. The arch plunges eastward from the northeast bulge of the Rock Springs uplift toward the Rawlins uplift and Sierra Madre uplift, but does not definitely join either of these latter structural elements. The stronger south flank of the arch dips into the Washakie segment of the Green River Basin. The north flank fades gradually into the Red Desert segment of the Green River Basin.

The stratigraphic section follows.

Eocene
Tipton tongue of Green River formation
Very gentle unconformity
Hiawatha member of Wasatch formation (minor gas)
Paleocene
Fort Union formation
Gentle unconformity
Upper Cretaceous
Lance formation
Lewis shale (with associated sandstones) (oil and gas)
Mesaverde group
Almond formation (oil and gas)
Ericson sandstone (minor gas)
Rock Springs formation
Blair formation
Baxter shale

Gas and oil has been found in the Mesaverde group, mostly in sandstones in the Almond formation. To a lesser extent production has been obtained from sandstones within the Lewis shale and near the Lewis-Lance transition zone and from the Ericson sandstone. There is also minor production indicated from sand lenses in the Hiawatha member of the Wasatch.

Table Rock anticline on the southeast flank of the arch is the only structure with demonstrable surface closure. Tertiary gas was discovered here in 1946 with deeper Lewis and Mesaverde discoveries in 1954. Discovery of major gas reserves at Desert Springs in 1958 triggered rapid expansion of exploratory and development drilling which continues to date. Major new field discoveries include Patrick Draw, Arch, Playa, and West Desert Springs. Productive areas have expanded across original Federal unit boundaries and have overlapped and coalesced, causing numerous problems in nomenclature.

Except for Table Rock, all fields discovered to date are stratigraphic traps with minor structural complexities. Usually the oil and gas is found trapped in closed sandstone bodies formed as offshore bars in the shallow Lewis and Almond seas.

The Wamsutter arch is a young upwarp (possibly Pliocene) superimposed across older Tertiary and late Cretaceous structural trends. The older structural patterns are, as yet, imperfectly known and understood.

End_of_Article - Last_Page 415------------