Early Proterozoic Geology of the Highland Mountains, Southwestern Montana, and Field Guide to the Basement Rocks that Compose the Highland Mountain Gneiss Dome part of MT Field Guides
The Highland Mountains are underlain by the largest of the northwesternmost exposures of basement crystalline rocks in southwestern Montana....Metasedimentary rocks in the Highland Mountains are in part lithologically similar to the Late Archean multilithologic sequence (in the Tobacco Root, Ruby, and the northern Madison and Gravelly Ranges), but are considerably thinner. In the Highland Mountains the individual beds of aluminous schist, marble, quartzite, and iron-formation extend for only short distances, but the assemblage as a whole is mappable. It nowhere exceeds 300 ft (100 m) in thickness and appears to pinch out to the north....these rocks in the Highlands, unlike those to the southeast, are overlain by more than 10,000 ft (3000 m) of aluminous biotite gneiss that may have been deposited as muds basinward from the Late Archean shelf edge.

Middle Proterozoic Belt Supergroup, Western Montana part of MT Field Guides
From Great Falls, to Butte, Helena Glacier National Park and Spokane, this field trip crosses onto the leading edge of the Rocky Mountain thrust belt and proceeds to the stratiform copper-silver deposits in the Revett Formation of the Troy Mine in the main part of the Belt basin. The road log includes sections on the paleontology of the Middle Proterozoic Belt Supergroup, stromatolites of the Belt Supergroup (specific to Glacier National Park), Middle Proterozoic Tectonics of the Belt basin, and a sedimentologic and tectonic interpretation of the Belt Supergroup.

Heart Mountain Detachment Fault and Clastic Dikes of Fault Breccia, and Heart Mountain Break-Away Fault, Wyoming and Montana part of MT Field Guides
This field guide describes the geology of two sites near Silver Gate, MT (near Cooke City) where different features related to the Heart Mountain detachment are displayed. At the first site, several features pertaining to the origin of the Heart Mountain detachment fault can be examined, including: (1) severely deformed upper plate rocks in contact with undeformed lower plate rocks; (2) the character and composition of the fault breccia; (3) contacts of volcanic rocks with upper plate blocks and the Heart Mountain fault; and (4) dikes of carbonate fault-breccia injected into both upper plate blocks and overlying volcanic rocks. The second site is an exposure of the Heart Mountain break-away fault.

Hydrologic Aspects of Metal Mine Impacts on Upper Clark Fork Superfund Sites, Butte - Warm Springs, MT part of MT Field Guides
This road log concentrates on environmental impacts of historic mining activities in the Butte Mining District, particularly with regard to water quality. The trip decribes the general geology between Bozeman and Butte and provides a detailed overview of the geology, hydrogeology, mineralization, and mining history in the Butte district. Specific topics included in this field guide are: water quality changes in underground mines and the Berkeley Pit, impacts and remediation of mine tailings and processing plants (mills, smelters, and reduction plants), and groundwater contamination and remediation. Detailed information from geotechnical and hydrogeological studies related to these topics is included.

Field Guide; Little Rocky Mountains part of MT Field Guides
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.

Crazy Mountains, Montana part of MT Field Guides
This trip examines a variety of mid-Eocene alkalic (feldspathoidal) stocks, laccoliths, sills, and dikes emplaced into Cretaceous and Paleozoic sedimentary strata. These rocks include mafic and felsic varieties, and are both texturally and compositionally variable. Most of the mafic alkalic rocks are unique in the Montana Alkalic Province in having Na2O > K2O. They are unusual even among feldspathoidal rocks because they are stongly enriched in incompatible elements, and have Sr, Nd, and Pb isotopic compositions which reflect an ancient source having low Rb/Sr, Sm/Nd, and U/Pb.

Geology of the Stillwater Complex Exposed in the Mountain View Area and on the West Side of Stillwater Canyon part of MT Field Guides
The part of the Stillwater Complex exposed on the west side of the Stillwater canyon has been the site of concentrated prospecting and geology activity since Jack Nye and Jimmy and Jonas Hedges found sulfide-rich rocks there in 1883. Readily seen in this area are well-studied and excellent exposures of: (1) most rock types, (2) ore deposits and mineralized occurrences, (3) structural features and (4) stratigraphic and age relations between the metamorphosed sedimentary rocks and the layered ultramafic-mafic stratiform intrusion. In addition, there are good exposures of a quartz monzonitic suite, which intrudes the complex and the metamorphosed sedimentary rocks, and of the Beartooth gneisses. Because the rocks in this area have been deformed by several episodes of faulting, a synopsis of the structural relations is given to clarify the geologic setting. Detailed overviews of the geology specific to the area are presented, and the geology of the more interesting exposures in the area is described in a road log that begins in the Ultramafic series, proceeds through the Basal series, the Banded series, and the quartz monzonite that cuts the complex, and ends in the Beartooth gneisses.

The Hebgen Lake Earthquake Area, Montana and Wyoming part of MT Field Guides
Several high-angle normal faults bounding the west front of the Madison Range north of Hebgen Lake, recurrently active during much of Neogene time, reactivated catastrophically on August 7, 1959. Faulting was accompanied by largest historic earthquake within the Intermountain Seismic Belt. Unusual geologic features were formed--spectacular fault scarps, a large landslide, a deformed lake basin (Hebgen Lake), and a new lake (Earthquake Lake)--each of which demonstrates the destructive power of a large eathquake. These features are described in the context of the bedrock geology in this field guide.

Great Falls to Wolf Creek (Via I-15) part of MT Field Guides
Great Falls is underlain by the Lower Cretaceous Kootenai Formation (Aptian), a series of red sandstones and shales which is considered to have been deposited in a "mostly" nonmarine environment. The city is on a crest of a broad northwest-plunging anticline called the South Arch, which lies just east of the Montana Thrust Belt. As we drive southwestward towards the Montanta Thrust Belt today, we will travel off the northwest flank of the South Arch. This will take us gradually from Lower Cretaceous to Upper Cretaceous outcrops until we reach the edge of the mountain front.

A Traverse Across the Central Belt Basin From Bowmans Corner, Montana to East Hope, Idaho part of MT Field Guides
This road log highlights a variety of sedimentary rock types and structures along a transect of the Rocky Mountain Fold and Thrust Belt. The log follows Montana Highway 200, which crosses the central part of the Middle Proterozoic Belt basin from the Montana disturbed belt to Missoula, where it turns northwesterly into northern Idaho, traversing rocks of the western and northwestern Belt basin. The road log begins east of the Rocky Mountain front in the disturbed belt underlain by soft, Cretaceous shale and somewhat more resistant sandstone units. Next, the road log passes into the eastern thrust belt where thrust faults bring Belt rocks first over Cretaceous, then over Paleozoic rocks, and finally over Proterozoic rocks farther to the west. At Rogers Pass, the route crosses the Continental Divide and into the Ovando block where Cenozoic listric normal faults form the major structures. The leading edge of the western thrust belt is encountered at Bonner, MT. From Missoula, Highway 200 trends northwestward to northern Idaho and diagonally crosses the western part of the Belt basin. Changes in grain-size and sediment type observable from outcrops along this road log illustrate the evolution of sedimentary transport and facies tracts within the central part of the Belt basin.