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Use this page to search our collection of educationally-useful geologic field guides and road logs in Montana and Yellowstone. You may search the database by entering a keyword to search or choosing one of the listed terms for geologic topic, geographic location, or geologic province.


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Depositional Surfaces in the Eagle Sandstone at Billings, Montana part of MT Field Guides
Marine shelf sandstones and barrier bars are commonly formed by lateral accretion of sand bodies with time lines inclined to the formation boundaries. Shelton (1965) described low-angle inclined bedding in the lowermost sandstone unit of the Eagle Sandstone at Billings, Montana. He recognized these beds as shoreface accretion surfaces of a barrier bar and likened them to those found on present-day Galveston Island, Texas. The Billings location provides an excellent opportunity to examine an important hydrocarbon reservoir rock of the Northern Rocky Mountain region.

Topics: Resources, Sedimentary rocks, Fossils
Geographic Location: South-Central Montana
Geologic Province: Montana Plains

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.

Topics: Sedimentary rocks, Igneous rocks, Surficial geology, Metamorphic rocks
Geographic Location: South-Central Montana
Geologic Province: Central Rocky Mountains Foreland Province

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.

Topics: Resources, Igneous rocks
Geographic Location: South-Central Montana
Geologic Province: Central Rocky Mountains Foreland Province

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.

Topics: Resources, Igneous rocks
Geographic Location: Southwest Montana
Geologic Province: Rocky Mountain Fold-Thrust Belt

Upper Cretaceous-Paleocene Sequence, Bug Creek Area, Northeastern Montana part of MT Field Guides
Study of the Late Cretaceous-Paleocene sequence in the Bug Creek Area and the rest of the Fort Peck Fossil Field has contributed greatly to our understanding of the paleoecology and stratigraphy of dinosaur extinction and the primary radiation of Tertiary placental mammals. The area features at least 133 species of spores and pollen, 93 species of Cretaceous vertebrates (including 30 species of mammals and 19 species of dinosaurs), 24 species of Paleocene mammals, as well as the oldest ungulate and primate specimens ever found. Fossil leaves and wood have also been described. The area also includes well-studied localities of the K/T boundary containing Ir-rich clay and shocked quartz. No section of terrestrial sediments across the K/T boundary has been studied in as many ways as this one. This has been and will continue to be a major locality at which to study evidence for various hypotheses about the events at the K/T boundary.

Topics: Sedimentary rocks, Fossils
Geographic Location: Northeast Montana
Geologic Province: Montana Plains

Structural Geology of the Sawtooth Range at Sun River Canyon, Montana Disturbed Belt, Montana part of MT Field Guides
The Sawtooth Range is one of the best exposed examples of imbricate thrust faulting in the foreland fold and thrust belt of the western United States. It is an outstanding field classroom for the demonstration of stratal shortening and the various structural features associated with thrust belt terranes. This 7-stop traverse through Sun River Canyon offers excellent exposures of thrust contacts along the road and panoramic views of stacked thrust sheets and demonstrates the dependence of structural style on relative competence of units in the stratigraphic section.

Topics: Structures, Sedimentary rocks
Geographic Location: Northwest Montana
Geologic Province: Rocky Mountain Fold-Thrust Belt

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.

Topics: Surficial geology, Hydrology, Sedimentary rocks
Geographic Location: Northwest Montana
Geologic Province: Rocky Mountain Fold-Thrust Belt

Geology Along Going-To-The-Sun Road, Glacier National Park, Montana part of MT Field Guides
This guide to the geology along Going-to-the-Sun Road in Glacier National Park describes many of the major geologic features of the Park. It is directed toward the Park visitor with little no no background in geology. The guide begins with a short introduction to the science of geology and the geologic time scale, followed by a simplified geologic cross section through the Park from SW to NE. The bulk of the field guide is a 21-stop road log, keyed to numered octagonal signs along the road, which describes the geology along the road. A glossary of geologic terms and an appendix is included which contains a brief geologic history of Glacier National Park, explanations of rock colors and fossil algae (stromatolites), and descriptions of the Proterozoic rock formations that can be seen along the Going-to-the-Sun Road. An extremely useful resource included at the back of the book is a fold-out geologic map, plotted on an oblique shaded-relief diagram, that depicts the landscape and the distribution of rock formations and faults in the vicinity of Going-to-the-Sun Road.

Topics: Metamorphic rocks, Sedimentary rocks, Igneous rocks, Structures, Surficial geology, Fossils
Geographic Location: Northwest Montana
Geologic Province: Rocky Mountain Fold-Thrust Belt

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.

Topics: Structures, Igneous rocks, Sedimentary rocks
Geographic Location: North-Central Montana
Geologic Province: Montana Plains, Central Rocky Mountains Foreland Province, Rocky Mountain Fold-Thrust Belt

Rhyolite-Basalt Volcanism of the Yellowstone Plateau and Hydrothermal Activity of Yellowstone National Park, Wyoming part of MT Field Guides
This field guide provides an overview of the major geologic and hydrothermal features along the park roads through the western and northern parts of Yellowstone National Park. A number of sites from Old Faithful to Mammoth Hot Springs are described in the context of the geologic history of the Yellowstone region. Areas receiving special emphasis are the Firehole River and Upper Geyser Basin (including the Old Faithful area), Midway and Lower Geyser Basins, Firehole Canyon, Madison Junction, Norris Geyser Basin, the Norris-Mammoth Corridor, and Mammoth Hot Springs.

Topics: Surficial geology, Structures, Hydrology, Igneous rocks, Sedimentary rocks
Geographic Location: Yellowstone National Park
Geologic Province: Yellowstone Plateau