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.

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.

Multiple Catastrophic Drainage of Glacial Lake Missoula, Montana part of MT Field Guides
This field guide describes two localities related to the history and drainage of Glacial Lake Missoula northwest of Missoula, Montana. The first site highlights spectacular erosional and depositional features that illustrate the effects of extremely large discharge related to the drainage of the lake. In a sense, the area is the world's most extravagant natural flume experiment. Features include bedrock basins (scoured by flood waters), large deltaic bars, and megaripples as large as 35 feet from crest to trough. The second site, a large roadcut along I-90, contains a record of at least 36 fillings of the lake, presumably during Pinedale(?) time, suggesting that drainage occurred many times. Another roadcut exposes a similar, but unstudied record of deposition in a higher terrace that probably formed during Bull Lake(?) time and may indicate an older history of lake formation and drainage.

Field Guide to the Mountain View and West Fork Areas, Stillwater Complex, Montana part of MT Field Guides
The Mountain View area of the Stillwater Complex, which is exposed on the west side of the Stillwater River valley, contains a well exposed, easily accessible section through the Ultramafic series. In this area the ultramafic cumulates have, for the most part, escaped the serpentinization common in other parts of the complex. The Basal series rocks and the lowermost ultramafic cumulates, however, have suffereed extensive alteration. The hornfels and the sill/dike complex are reasonably fresh and well exposed in the Verdigris Creek area, the site of intensive exploration for Cu/Ni sulfides. The Banded series rocks are well exposed along the mine road leading to the abandoned Mouat chromite mine, although only Lower Banded series cumulates are present in this area.

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.

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.

Guide to the Picket Pin Mountain Area part of MT Field Guides
This traverse through part of the Banded series provides relatively easy access to the upper half of the exposed part of the Stillwater Complex. The percentage of outcrops is high, and even in areas of soil or tundra cover, the float appears to be sufficiently immobile and concentrated to give an accurate picture of the underlying bedrock geology....The traverse begins in the Middle gabbro zone and terminates where Paleozoic limestone unconformably overlies the Upper anorthosite zone. Above the Middle anorthosite zone, it follows the Picket Pin section described by McCallum and others (1980) and Raedeke (1982b)....An optional traverse through some lithologically complex and intriguing rocks in the Upper anorthosite zone north of the Castle Creek fault is also described. Total traverse time, including the drive from Carter's Camp and return, is 8-10 hours. Elevations range from 9,300 to 10,000 feet.

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.

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.