The Northern Pacific Railroad Company well No. 1, drilled with rotary tools in 1935-1936 by the Montana-Dakota Utilities Company to the depth of 8,186 feet on the Baker-Glendive anticline of eastern Montana, following geophysical exploration of the subsurface, revealed that strata above the Pennsylvanian are similar to those of the Black Hills section except that 350 feet of salt was found in the Spearfish formation (or possibly the Permian). However, between the top of the Minnelusa formation at 5,631 feet and the top of the Madison at 7,440 feet, there are present 1,325 feet of beds representing the Big Snowy group of central Montana, as described in 1935 by H. W. Scott. The Madison appears to extend to a depth of about 8,055 feet, and the strata below that depth may re resent the Devonian. Considerable help with correlations was offered by a restudy of samples from the Sinclair Prairie Oil Company's Westphal well drilled in 1931 on the Porcupine dome, 135 miles northwest of the Northern Pacific well.

It appears that the Big Snowy geosyncline of Mississippian age extends east at least to the Northern Pacific well No. 1 and has a length of at least 375 miles.

Oil was produced from the Northern Pacific well between 6,747 and 6,796 feet from the Big Snowy formation, and also from 8,130 to 8,186 feet from beds that may be Devonian in age.