Pg. 679, figs. 2, 3. Hellgate formation of Missoula group. Type section (on north side of Mount Sentinel, the south wall of Hellgate Canyon) consists of (descending): (1) massive, gray-red siliceous quartzite, weathering variegated gray, buff, and lavender, 365 feet; (2) massive gray and red gray fine- to coarse-grained finely banded pure quartzite and sandy quartzite, ripple marked, 280 feet; (3) massive thick-bedded pink-gray quartzitic sandstone, weathering buff, 1,160 feet; (4) massive, gray, fine-grained, siliceous quartzite, ripple-marked, weathering buff, 300 feet; (5) massive red-gray coarse-grained quartzite, with sandy beds up to 3 feet in thickness, weathering buff and dull lavender, 95 feet. Conformably underlies McNamara formation and unconformably(?) overlies Miller Peak formation; all included in Missoula group. Recognized in central western Montana (Missoula to Helena). Age is pre-Cambrian (Belt).

Source: US geologic names lexicon (USGS Bull. 896, p. 938).

Pg. F195 (fig.), F198; USGS Misc. Inv. Ser. Map I-296, 1959. Hellgate quartzite member of Miller Peak quartzite of Missoula group. Rank reduced to member status in upper part of Miller Peak quartzite. Thickness about 1,200 feet on University Mountain. Underlies about 1,000 feet of argillite previously assigned to lower member of McNamara formation by Clapp and Deiss. Age is Precambrian (Belt).

Source: Publication; US geologic names lexicon (USGS Bull. 1200, p. 1726).