Mendenhall Formation of Interlake Group (subsurface of MT,ND)
Silurian
Type section (subsurface): depth-interval 11,785 to 12,220 ft, Amerada No. 1, Mendenhall Unit No. 9 well, in sec. 9, T. 154 N., R. 95 W., Williams Co., ND (Megathan, 1987).
Williston basin
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