A report about gold mineralization at the Golden Sunlight breccia pipe, southwestern Montana, is related to emplacement of Late Cretaceous alkali-calcic rhyolite and subsequent collapse of the Belt Supergroup wallrock and rhyolite in the pipe.

From introduction: acknowledgements.-The Forsyth field was examined to collect data upon which to classify the public land included in it with regard to its value as coal land. The geologic mapping was done with the plane table and telescopic alidade, and all locations were tied to land corners.

From introduction: This report is a guide to the geology and scenery of Glacier National Park.

From introduction: The discovery of oil near Kevin, Mont., in March, 1922, gave prominence to the Sweetgrass arch, which is a large structural uplift somewhat similar in size and degree of folding to the Cincinnati arch. Most of the development so far attempted on this fold has been on the Kevin-Sunburst dome, a bulge upon the crest of the arch just south of the Canadian boundary. The dome covers about 16 townships, is nearly circular in outline, and has very low dips away from its highest point in all directions. Within the last five years (1923-1927) about 1,500 wells have been drilled upon it, over 880 of which are rated as productive. Since May, 1925, the field has stood second in production in the Rocky Mountain States being exceeded only by Salt Creek.

From introduction: This report details the results of a geological survey of the Libby Quadrangle, Montana.

From introduction: This report contains information concerning the geology of Big Horn County and the Crow Indian Reservation and their resources in ground water, coal, oil, and gas. These facts were collected in the course of studies for about a dozen field projects, which ranged in character from reconnaissance studies of large areas to very detailed mapping of certain tracts to show the occurrence of oil and gas. Consequently, the information at hand, either as to the geology or the resources, is not equally complete and definite for all parts.

From abstract: The origin of the gneissic rocks on the eastern border of the Idaho batholith in the Bitterroot Range, near Hamilton, Mont., has long been in dispute. Lindgren regarded these rocks as the product of stresses related to a normal fault along the front of the range with an eastward dip of about 150. He thought both the hanging wall and the footwall had moved, with a total displacement along the fault plane of at least 20,000 feet. The faulting was believed to have been so recent as to be a major factor in the present topography. Langton appears to accept the concept of faulting but to regard the gneissic rocks as formed much earlier from a granitic rock that was more silicic and older than the Idaho batholith.

From abstract: A mineral resource survey of the Ruby Mountains Wilderness Study Area (MT-076-001) was made in 1984- 85. Thirty-two million tons of subeconomic mineral resources that average 21 percent iron occur in the Kelly iron deposit and constitute an identified resource adjacent to the southeasternmost edge of the study area. Moderate and high mineral resource potential for talc deposits occur within a large body of Archean (see geologic time chart in appendix) marble in the central part of the study area (fig. 1). The study area has a low mineral resource potential for uranium and for oil and gas sources. No phosphate deposits exist in the study area.

From summary:A mineral resource survey of a 10,610-acre part of the Blacktail Mountains Wilderness Study Area (MT-076- 002) was conducted in 1984-85. Identified subeconomic resources of barite exist in the area at the northernmost boundary, and a zone partly within the area along the northeastern boundary has a moderate mineral resource potential for silver and barite, and associated gold, copper, lead, and zinc. No producing mines occur in or adjacent to the area. The area lies within a region that is rated as having moderate energy resource potential for oil and for gas.

From abstract: A mineral resource survey was conducted in 1987 by the U.S. Geological Survey and the U.S. Bureau of Mines to evaluate mineral resources (known) and mineral resource potential (undiscovered) of the Sleeping Giant Wilderness Study Area (MT-075-111) in Lewis and Clark County, Montana. The only economic resource in the study area is an inferred 1.35-million-ton reserve of decorative stone (slate); a small gold placer resource is subeconomic. A high resource potential for decorative slate exists directly adjacent to the area of identified slate resource and in the northeastern part of the study area. The rest of the study area has a low potential for decorative slate. The westernmost part of the study area has a moderate resource potential for copper and associated silver in strata-bound deposits in green beds and limestone; potential is low in the rest of the study area.

From introduction: The detailed information concerning the coal deposits of the Ashland field set forth in this report has been obtained in the course of an investigation that has been conducted both as a part of the United States Geological Survey's general systematic study of western coal lands and as an aid in the administration of the public lands. With the information obtained on the location of outcrops, the number, distribution, and thickness of coal beds, the accessibility of the coal, and the thickness of the overburden, the public lands of the region are classified as to their coal value; coal-bearing lands are differentiated from noncoal-bearing lands; and the administration of the coal-land leasing law is facilitated.

From abstract: The uppermost Cretaceous Lance Formation was studied in the Powder River Basin and nearby basins of Wyoming and Montana. The Lance Formation is overlain by the continental Paleocene Fort Union Formation. This report is a petrography and stratigraphy study on these basins.

From abstract: This report is a study on the history of sedimentology and deposition of the lower Paleocene Tullock Member of the Fort Union Formation, Powder River Basin, Wyoming and Montana while looking at the geometry and sedimentary structures.

From abstract: This report describes Cambrian through Mississippian rocks in the Powder River Basin representing five depositional sequences that reflect both the biological evolution and the tectonic development of western North America.

From abstract: This report contains complete Bouguer anomaly, isostatic residual anomaly, and horizontal gradient anomaly gravity maps of the Powder River Basin and surrounding areas in southeastern Montana, northeastern Wyoming, and western South Dakota were compiled using gravity data from 21,528 stations. A total-intensity anomaly aeromagnetic map with 3 mile spaced east-west flight-lines is also presented. Also included is an analysis of these maps and data, focusing on gravity and aeromagnetic studies.

Abstract: The Farlin Creek Wilderness Study Area (MT-076-034) is in the south-central Pioneer Mountains about 24 miles west-northwest of Dillon, Beaverhead County, southwestern Montana. At the request of the U.S. Bureau of Land Management, an area of 610 acres (less than 1 square mile) was investigated by the U.S. Geological Survey and the U.S. Bureau of Mines in 1984. The area contains no mines or prospects, no visible evidence of mineralization, and no identified mineral resources. Geophysical evidence suggests that three parts of the area have moderate mineral resource potential for undiscovered resources of molybdenum. The entire area has a low resource potential for all other metals and for all nonmetals, fuels, and geothermal energy.

The following report presents measured sections and lithostratigraphic correlations of the units in the order to document a syntectonic unconformity in order to understand the tectonic history of the area.

The following report analyzes geological studies on surficial deposits in the Sheridan quadrangle of Wyoming and Montana.