IDAHO GEOLOGICAL SURVEY MOSCOW-BOISE-POCATELLO
TECHNICAL REPORT 06-2 RODGERS AND OTHERS Sheet 1 of 2 sheets
Geologic Map Of The Inkom Quadrangle, Bannock County, Idaho
D. W. Rodgers, S.P. Long, N. McQuarrie, W. D. Burgel, and C. F. Hersley 2006
E
Ql Zcu
33 40 50 72 39 46 57
Correlation Of Map Units
Qfp Qal Qbg Ql/Qfgw Qp Ql
Holocene Upper Pleistocene Middle Pleistocene Lower Pleistocene
Zm Zm
Quaternary
This Technical Report is a reproduction of independent mapping by D.W. Rodgers, S. P. Long, N. McQuarrie, W.D. Burgel, and C. F. Hersley of Idaho State University. Its content and format may not conform to agency standards.
unconformity
Cenozoic
Zi Zi
Upper Miocene
MUTUAL FORMATION (Late Proterozoic)--Quartzite with uncommon shale and pebble conglomerate interbeds. Quartzite is medium- to thick-bedded, pink to purple, medium-to coarsegrained, well rounded, moderately to poorly sorted. Its protolith was probably a subarkosic to sublithic arenite. Pebble conglomerate is poorly sorted, with purple, pink and red clasts in a white to purple matrix. Shale is fine-grained, dark purple and occurs rarely as interbeds. The lower contact is placed at the base of the lowest purple quartzite. Link et al. (1987) interpret the lower contact as a regionally persistant sequence boundary. Unit is resistant, but rarely forms small ledges and occurs mostly as float. Minimum thickness is 900m (3000 ft). INKOM FORMATION (Late Proterozoic)--Shale and siltstone. Fine-grained, thin-bedded to laminated, and olive green except at top where it becomes dark purple. Lower contact is placed at top of highest quartzite or conglomerate. Non-resistant beds form uncommon small ledges. Thickness about 250m (825 ft). CADDY CANYON QUARTZITE, UPPER MEMBER (Late Proterozoic)--Quartzite and conglomerate with minor thin-bedded shale. Pebble conglomerate is located at top of member and contains numerous white to pink quartzite pebbles. Base of conglomerate was interpreted by Link et al. (1987) as a regionally persistant sequence boundary. Quartzite is thick-bedded to massive, pink, red, maroon and rarely purple, fine- to mediumgrained, and moderately to well sorted. Its protolith was probably a subarkosic arenite. Lower contact of upper member placed at base of discontinous thin-bedded olive green shale, at top of discontinuous limestone, and/or at base of red quartzite. Forms small blocky outcrops with talus. Thickness ranges from 600m (2000 ft) north of Portneuf Gap to 400m (1300 ft) south of Portneuf Gap. CADDY CANYON QUARTZITE, LOWER MEMBER (Late Proterozoic)--Quartzite with uncommon shale. Quartzite is massive to thick-bedded, white to beige, vitreous, moderately sorted, well rounded, and fine- to medium-grained. Its protolith was a quartz arenite. Shale is tan to olive, thinly bedded and coarsens upward to sandstone. Lower contact is placed at base of lowest quartzite. Forms a resistant cap on hilltops and blocky float. Thickness ranges from 700m (2300 ft) north of Portneuf Gap to 500m (1650 ft) south of Portneuf Gap. PAPOOSE CREEK FORMATION (Late Proterozoic)--Intercalated argillite and quartzite. Argillite is dark gray to green to rust colored. Quartzite is light gray to brown, fine-grained and well sorted. Thinly interbedded argillite and quartzite are distorted by common syneresis structures and other soft sediment deformation. The gradational lower contact is placed at the top of the highest limestone bed. Forms low ledges. Thickness ranges from 280400m (925-1320 ft). BLACKROCK CANYON LIMESTONE (Late Proterozoic)-Limestone or dolomite marble with intercalated quartzite and shale. Limestone and dolomite are dark gray, massive (upper half) or medium-bedded (lower half) with small resistant lamina of sandstone or chert. Occurs as interbeds or lenses within finegrained laminated quartzite in the lower half or shale and siltstone (similar to Papoose Creek Formation) in the upper half. Lower contact is placed at base of lowest limestone. Forms ledges and slopes. Thickness ranges from 180-350m (600-1150 ft). POCATELLO FORMATION (Late Proterozoic)--Interbedded metavolcanic rocks, metadiamictite, quartzite, conglomerate, limestone and argillite. Divided into three members, in descending order the upper member, Scout Mountain Member, and the Bannock Volcanic Member.

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