Field Guide, Little Belt Mountains part of MT Field Guides
This field guide extends from Monarch to Utica across the northeastern portion of the Little Belt Mountains. The trip, via Hughesville, Yogo Peak and the Yogo sapphire mines, provides an overview of Laramide igneous activity in the Little Belt Mountains of central Montana. The mountains were formed as a large anticline in the Late Cretaceous to late Paleocene or earliest Eocene. The forceful intrusions in the Little Belt Mountains by felsic, hence viscous magmas, contrast sharply with the low-viscosity, basic, alkaline extrusives in the Highwood Mountains to the north.

A Traverse Across the Northern Belt Basin From East Glacier Park, Montana to Bonners Ferry, Idaho part of MT Field Guides
This field guide examines differences between three segments of the Belt Basin along an east-west transect from East Glacier Park, Montana to Bonners Ferry, Idaho. Each segment is characterized not only by its structural style, but also by the suite of Belt rocks that comprise it. The easternmost segment consists of the Lewis thrust plate and associated thrusts as far west as Columbia Falls, Montana where it is terminated by the Rocky Mountain trench. This segment contains eastern Belt facies including: Altyn, Appekunny, Grinnell and Helena (Siyeh), Snowslip, Shepard, Mount Shields and McNamara formations. Fine sediments in these rocks, probably derived from a western continental source terrane, were deposited adjacent to the stable North American craton, where they were mixed with smaller amounts of coarse sand derived from an inferred coarse sand sheet that mantled the crystalline craton. The central segment extends from the Rocky Mountain trench to the Libby thrust system. It is characterized by broad, open folds that expose Belt rocks of the central part of the basin, including a thick section of Prichard, Burke, Revett, St. Regis, Empire, Wallace and Helena formations. These rocks are composed mostly of argillite, carbonate and fine-grained quartzite. The western segment includes the Libby thrust and Leonia fault system. It extends as far west as the Purcell trench. Exposed in this area are rocks from the Prichard through the Missoula Group. Rocks of the Ravalli Group and the Wallace Formation contain more fine-to medium-grained quartzite than those of the central segment, reflecting a western source. However, the Missoula Group rocks are finer grained and more calcareous than those of the type area, indicating that late in the Middle Proterozoic the western source terrane probably subsided and that the basin center shifted westward.

A Traverse Across the Eastern Belt Basin From Neihart to Townsend, Montana part of MT Field Guides
This road log focuses on Precambrian (Proterozoic) sedimentary rock deposited in the Helena embayment of the eastern Belt basin. It also includes a general description of the geology between exposures of Proterozoic strata, briefly describing occurrences of Precambrian igneous and metamorphic rocks, Paleozoic sedimentary rocks, and Tertiary igneous rocks. A stratigraphic column is provided for refeference.

Road Log to the Picket Pin Mountain, Chome 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.

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.

Guide to the Benbow Area part of MT Field Guides
The Benbow area (named for T.C. Benbow, who first discovered chromite there) is at the east end of the exposed Stillwater Complex....Most of the localities described...are in the Ultramafic series....The features emphasized at these localities include the nature of the cyclic units, pegmatoids associated with chromite seams, evidence for slumping anbd slope instability in the Stillwater magma chamber, lateral persistence of some of the chromite seams, and the unconformity between the Banded series of the Stillwater Complex and overlying Cambrian limestone.

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.

Great Falls to Wolf Creek 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.

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.

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.