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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.


Results 31 - 40 of 54 matches

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.

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

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.

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

Field Guide to an Archean Transect, Eastern Beartooth Mountains, Montana-Wyoming part of MT Field Guides
The eastern Beartooth Mountains of Montana and Wyoming contain a record of crustal evolution that spans almost 1000 Ma and culminates in a major episode of crustal growth 2700-2800 Ma. The earlier record is sparse and complex as a result of extensive magmatism and intense metamorphism associated with Late Archean activity. In general, however, it appears that continental material was present in this area by roughly 3600 Ma, and that a stable continental shelf accumulated quartzites, iron-formation, and lesser amounts of pelitic to psammitic units interspersed with small volumes of mafic to silicic volcanic rocks. This cycle of accumulation was apparently terminated by an episode of granulite facies metamorphism 3300-3400 Ma, perhaps as a result of continent-continent collision....About 2800-2900 Ma, a second major cycle of crustal growth began that bears some resemblance to those associated with modern continent-ocean subduction zones....The first igneous rocks produced during this cycle were andesitic or dioritic rocks, both coarse and fine grained, that were subsequently metamorphosed to amphibolite facies....This interval is restricted by the presence of a granodioritic series (Long Lake granodiorite) that was intruded late in the kinematic cycle... (2779 Ma)...and marks the lower limit for the last major episode of regional metamorphism. The last and most volumetrically important rock produced during the cycle was the Long Lake granite. This unit composes approximately 80-90% of the eastern portion of the range and engulfs all older rock types. It appears to have been intruded about 2740 Ma....This excursion will attempt to view the evidence of these two major cycles in four main stops: (1) Hellroaring Plateau, (2) Lower Quad Creek, (3) Upper Quad Creek, and (4) Long Lake. Late Archean mafic dikes (at Beartooth Lake) will also be examined.

Topics: Metamorphic rocks, Igneous rocks
Geographic Location: Southwest Montana
Geologic Province: Central Rocky Mountains Foreland Province

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.

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

Yellowstone and Grand Teton National Parks and the Middle Rocky Mountains part of MT Field Guides
This trip is designed to show participants the granite-cored Laramide (Late Cretaceous-earliest Eocene) mountain ranges in the middle Rocky Mountains, and their various stages of burial by Cenozoic deposits and subsequent Quaternary exhumation. Mountain-flank structures involving Precambrian, Paleozoic, and Mesozoic rocks, the classic Heart Mountain detachment fault complex, and the rootless overthrust mountain ranges of the Wyoming-Utah-Idaho thrust belt are traversed.

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

The Yellowstone Plateau-Island Park Region part of MT Field Guides
The Yellowstone Plateau, at the center of one of the Earth's largest volcanic fields, spans the continental divide between the Northern and Middle Rocky Mountains at an average elevation of about 2.400 m. The eruptions of the Yellowstone Plateau volcanic field, entirely postdating 2.5 Ma, were exceedingly voluminous but are only the surficial expression of the emplacement of a batholithic volume of rhyolitic magma to high crustal levels. Although the latest eruptions were about 70,000 years ago, an immense hydrothermal system and a variety of geophysical characteristics indicate the continued presence of an active shallow magma chamber.

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

Glacial Lake Missoula: Sedimentary Evidence for Multiple Drainages part of MT Field Guides
Route Start point Missoula, MT End point Camas Prairie, MT Roads I-90, U.S. 93, Montana 200, Montana 382 Total distance Geology Summary This field trip guide briefly describes the possible origin of the ...

Bones and Rocks of the Upper Cretaceous Two Medicine-Judith River Clastic Wedge Complex, Montana part of MT Field Guides
The purpose of this field trip is to provide an overview of the paleontologic, stratigraphic, and paleoenvironmental aspects of the Upper Cretaceous Two Medicine-Judith River clastic wedge in western Montana. Strata of the Two Medicine Formation yielded the first evidence of such dinosaur social behavior as nest construction and parental care, and have provided important information concerning the processes of bonebed formation in the fossil record. The correlative Judith River Formation in Montana has yielded an abundant and diverse dinosaur fossil record primarily preserved as transported and concentrated accumulations of vertebrate remains ("microsites"). The geology and paleontology of four fossil localities [Seven Mile Hill, Shield's Crossing, Willow Creek Anticline (Egg Mountain), and the Badger Creek/Two Medicine River confluence] are described, but precise details concerning the locations of the sites are not given in the field guide.

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

Quaternary Geology and Faulting of the Helena Valley, Montana part of MT Field Guides
This field trip will give the participants an overview of the Quaternary deposits and late Cenozoic faulting which have shaped the Helena valley. The Helena valley is a NW-trending graben surrounded by bedrock highlands. Most of the western half of the valley is a young alluvial plain formed of coalescing alluvial outwash fans issuing from drainages flowing towards Lake Helena. The western valley is ringed by older pediment surfaces sloping gently down from the valley margins. The eastern half of the valley is underlain primarily by later Tertiary silts, sands and gravels uplifted and segmented by normal faulting. Atop these Tertiary deposits along the southern valley margin, early Quaternary alluvial deposits are preserved as hilltop remnants of a formerly much larger deposit. Late Cenozoic faulting shaped the Helena valley, creating the modern topography and influencing sedimentation patterns; however, only a few faults show evidence of late Quaternary offsets.

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

Economic Geology of the Greater Helena Area: Helena to Montana Tunnels Mine, Lump Gulch, Grizzly Gulch, Fort Harrison and Marysville part of MT Field Guides
The Helena area has a long history of base- and precious-metal production from the Corbin-Wickes District on the south to the Marysville gold district northwest of the Capitol City. Gold has also been mined from the placers along Last Change Gulch now within the city limits. This field trip examinations the volcanic-hosted ore body at the recently opened Montana Tunnels mine south of Helena. From this mine, participants will travel north to Helena through an area of numerous inactive base- and precious-metals mines at the northern margin of the Boulder batholith and then onto the Marysville district northwest of Helena where the gold deposits are related to the Marysville stock.

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