Pg. 39 and passim. Gordon Mountain limestone. Gray to chocolate-gray massive limestones underlying Switchback limestone and overlying Pentagon shale. Thickest (272 feet) in Dearborn area; thinnest (140 feet) in Wall Creek area [northwestern Montana]. Most distinguishing characteristic is the number of green shale zones interbedded at irregular intervals in the limestones. Age is Middle or Late Cambrian.
Forms top of central and principal peak of Gordon Mountain, [in sec. 10, T. 19 N., R. 13 W., Pilot Peak 7.5-min quadrangle, Powell Co., northwestern MT].
Type locality: middle part of the cliffs which form lower part of eastern side of a peak 8,300 ft elevation, the top of which is just 1 mi S. 48 deg. E. of top of Pentagon Mountain, [in sec. 14, T. 25. N., R. 12 W., Pentagon Mountain 7.5-min quadrangle, Flathead Co., northwestern MT].

Source: US geologic names lexicon (USGS Bull. 896, p. 842).

Pg. 1089; GSA Spec. Paper 18, p. 35, 100, 1939. †Gordon Mountain limestone. Name dropped from sequence of Cambrian formations recognized in northwestern Montana. Steamboat limestone, as used in 1933 sequence, has proved to be part of massive upper Dearborn limestone which was repeated in the Dearborn section by low-angle overthrust. Therefore, rocks to which name Steamboat was applied do not exist, and this name is freed for use and here applied to limestone and shale formerly designated Gordon Mountain limestone, which lies between the Pagoda or Pentagon and overlying Switchback formation. Age is Middle or Late Cambrian.

Source: US geologic names lexicon (USGS Bull. 1200, p. 1548).