Field Guide; Little Rocky Mountains
Route
Start point
U.S. Highway 191, miles post 109.1
End point
Zortman, Montana
Roads
U.S. 91, Montana 236
Total distance
25.2 miles
Geology
Summary
This fieldtrip examines deformed Paleozoic sedimentary rocks on the margins of the Little Rocky Mountains, Tertiary intrusive rocks (porphyrys, magmatic-hydrothermal breccias, and dikes), and associated mineralization.
Key Lithologic Features
- Mississippian limestone
- Mission Canyon Formation
- Lodgepole Formation
- Archean gneisses
- Tertiary syenite porphyry
- Sullivan Park porphyry
- Antoine porphyry
- Precambrian amphibolites
- Archean schist
- Eocene volcanics
- hypabysal intrusions
- Emerson Formation
Structures
- Great Falls tectonic zone
Landforms
Other Features
Reference
Russell, C.W., and Gabelman, J., 1991, Field Guide; Little Rocky Mountains,
in Baker, D.W., and Berg, R.B., eds.,
Guidebook of the central Montana alkalic province: Geology, ore deposits and origin , Montana Bureau of Mines and Geology Special Publication 100, p. 185-194.
Availability
Out of print; can be photocopied for a fee. For more information, search for
this publication's record at the MBMG.