Named as the middle member of Piper formation. Type section is interval from 4,618 to 4,687 in the Murphy Corporation No. 1 Firemoon well, center SE1/4 SE1/4 sec 12, T30N, R41E, Valley Co, MT in the Williston basin. Consists of 69 ft of buff to brown, dense to earthy limestone in type section, which is typical of member throughout much of northern and eastern MT. Locally becomes sandy and oolitic. In some wells, member is dolomitic and cherty, especially on east flank of Sweetgrass arch. In south-central MT, unit is thinly bedded with much varicolored claystone and locally some gypsum. Pebbly oolitic and coquinoid limestones common. Very uniform in thickness. In outcrop sections, member appears transitional with underlying Tampico shale member (new) and overlying Bowes member (new), but in subsurface of northern MT and stratigraphic boundaries generally sharp. West and south of Bearpaw Mountains, it overlaps Tampico member and unconformably rests on Madison limestone. Occasionally in contact with Amsden formation on Big Snowy platform. Unit is correlative to middle limestone member of Piper as described by Imlay and others (1948). Is Middle Jurassic in age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Is middle member of Piper Formation, central and eastern MT and western ND, in Williston basin. Summarizes lithology, basis for dating, distribution, and correlation. Is Middle Jurassic (Bajocian) in age.

Source: GNU records (USGS DDS-6; Denver GNULEX).