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.

The Middle Yellowstone Valley from Livingston to Gardiner, Montana: A Microcosm of Northern Rocky Mountain Geology part of MT Field Guides
The middle Yellowstone valley, between the Great Plains at Livingston and the edge of the Yellowstone volcanic plateau near Gardiner, is a complex palimpsest of lithology, structure, and surficial processes. It shares basement rocks with the continental interior, largely to the north and east; Paleozoic lithologies with the western interior, compressive tectonics with the Fold and Thrust Belt to the west; extension with the Basin and Range to the west and south; and Cenozoic volcanism and elements of its geomorphic evolution with much of the surrounding region. The geological exploration of this region serves as a microcosm of the evolution of the geological understanding of the American West.

Shonkin Sag and Square Butte Laccoliths, Montana part of MT Field Guides
Shonkin Sag and Square Butte laccoliths are at the eastern edge of the Highwood Mountains as part of the Central Montana Alkalic Province. Rocks in the Highwood Mountains date to 50-53 Ma. Both laccoliths are internally differentiated and contain a variety of rock types, including shonkinite, syenite, and pegmatite.

The Stillwater Complex, Southern Montana; A Layered Mafic Intrusion part of MT Field Guides
Layered complexes provide the most visible evidence of processes of magmatic differentiation; thus, they occupy a central place in the study of igneous petrology. Such complexes are not only scientifically rewarding, they are host to several types of mineral deposits, including copper-nickel, chromium, and platinum-group elements. The Stillwater Complex is one of the world's great layered mafic intrusions, distinguished not so much by its size as by the fact that it is tilted on its side, and erosion has exposed the layering to ready access. This fieldguide presents a summary of the geology of the complex in the Benbow and Mountain View areas. The Benbow area offers easy access to a variety of rocks from the ultramafic series and chromite deposits but only limited exposures of features from the banded series. The Mountain View area offers easy access to most of the banded series and the platinum deposits.

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 Butte Mining District part of MT Field Guides
The Butte mining district is one of the major mining districts of the world with continuous production from both underground and open pit mines for 119 years, from 1864 to 1983. During this time, mining activites at Butte have introduced many firsts in mining methods, techniques of mine mapping, and the detailed recording of geologic data. This field guide describes the geology of the mineral deposits, provides a geologic map of the district, and concludes with a tour of eight locations of interest, including Alice pit, Syndicate pit, Berkeley pit, the Emma and Orphan Boy veins of the Anaconda system, the World Museum of Mining, and the Montana Tech Mineral Museum.

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.

A Study in Contrasts: Archean and Quaternary Geology of the Beartooth Highway, Montana and Wyoming part of MT Field Guides
Nowhere in the U.S. are the oldest and the most recent aspects of geology as spectacularly displayed as along the Beartooth Highway. The Beartooth Mountains are a block of largely Archean bedrock uplifted along high-angle reverse faults of Laramide age. The Precambrian rocks (3400-700 Ma) contain one of the best records of the early history of the igneous and metamorphic basement of the middle Rocky Mountains. These rocks include granulite-facies supracrustal rocks proposed as products of continental collision, calc-alkaline volcanic and plutonic rocks generated along an Archean continental margin, and mafic dikes some of which were emplaced during continental rifting. This Precambrian record encompasses at least two extensive periods of crustal evolution and records more geologic history at one location than any other place in the Wyoming Province. Descriptions of two key areas showing the fundamental relations between the Precambrian rocks are included: the Quad Creek area and the Long Lake area. The Beartooth Plateau has been extensively sculpted by glacial processes during the Pleistocene. The highway crosses a classic locality of "biscuit-board topography"--plateau remnants partially dissected by cirques--as well as deposits left by glaciers that etched the plateau. Features to be seen include glacio-fluvial terraces showing downstream effects of the glacial system and extensive areas of periglacial features that postdate glaciation. Glacial features are described from the Red Lodge area, Rock Creek Canyon, the hairpin turns, the Beartooth Plateau, and the Clark Fork basin.

Road Log to the Picket Pin Mountain, Chrome Mountain and Contact Mountain Areas part of MT Field Guides
This road log describes the geologic features along the access roads for three additional traverses: Guide to the Picket Pin Mountain Area, Guide to the Chrome Mountain Area, and A Traverse Through the Banded Series in the Contact Mountain Area. "This trip requires nearly 2 hours without stops. Beyond 12.5 miles, the road is rough and steep in places; a four-wheel-drive vehicle is recommended.