There were no major discoveries of oil and gas in unproved areas in the Rocky Mountain district in 1940, most of the drilling being restricted to inside locations in major fields.

In Wyoming, good showings of oil encountered in the Shannon sandstone member of the Steele shale (Upper Cretaceous) in the Cole Creek field during deeper drilling in 1937 and thereafter, were tested further in 1940 and commercial production found; one relatively small oil well was drilled in the North Labarge field, Sublette County, 2½ miles north of the nearest production in the Labarge field; and wells deepened a few feet in the Tensleep sandstone (Pennsylvanian) in the Mahoney field, Carbon County, and to the basal member of the Tensleep in the Lost Soldier field, Sweetwater County, were good oil wells. During 1940, commercial amounts of oil were first found in the Tensleep in the East Mahoney (West Ferris) field, Carbon County. No new producing zones were found elsewhere in t e Rocky Mountain district during 1940. However, in February 1941, commercial amounts of oil were first found in the Sundance formation (Upper Jurassic) in the Wilson Creek field, Rio Blanco County, Colorado.

In Wyoming, the Frannie field, Park County, was extended almost ½ mile northwestward into Carbon County, Montana; Sundance production was extended eastward about ½ mile in the Lance Creek oil field, Niobrara County; the present north end of the Labarge oil field was extended westward by relatively active drilling; and Tensleep sandstone production was extended about ¼ mile northeast inthe Wertz oil field, Carbon County. Gas production in the Frontier sandstone (Upper Cretaceous) was extended about ½ mile northwestward in the Muskrat field, Fremont County, and almost ½ mile southeastward in the near-by Big Sand Draw field. In the Hiawatha field, Sweetwater County, commercial gas was found in the Wasatch formation (Eocene) about a mile north of the nearest produ er.

In Colorado, a good Morrison (Upper Jurassic) sand well was found in the Wilson Creek oil field, Rio Blanco County, 3/4 mile southwest of the nearest producer; and on the east side of the Hiawatha oil and gas field, Moffat County, one relatively large oil well and one relatively small one were found in sandstones of the Wasatch formation.

During the year, very few important wildcat wells were drilled in the district. In Montana, a 7,116-foot dry hole was drilled through the Sundance sand on the Absarokee structure, Stillwater County. In Wyoming, a 6,302-foot dry hole was drilled to Pennsylvanian beds in the Middle Baxter Basin area, being the first well to test certain lower zones in the Rock Springs uplift; a 4,243-foot dry hole was completed in the Deadwood formation (Cambrian) on the Bull Creek structure, Crook County; and an 8,343-foot dry hole was completed in the Tensleep sandstone on North Geary dome, Natrona County.

A new depth record for drilling in Wyoming was established at 10,121 feet in the Badger Basin field, Park County.

Several relatively short pipe lines were completed in the district during 1940, one of the larger being the 100-mile line between the Billy Creek gas field, Johnson County. Wyoming, and the Big Sand Draw gas line at Casper.