Report presenting new data on the age of the Boulder, Philipsburg, and Idaho batholiths of western Montana.

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: During fiscal years 1978 through 1981, the U.S. Geological Survey contracted for the acquisition and analysis of hydrologic data from 104 surface water stations, 26 ground water stations, and 15 precipitation gages as well as for several hundred miscellaneous surface water measurements of flow and water quality. The work was performed in Montana, North Dakota, Wyoming, Utah, New Mexico, and Oklahoma, terminating at the end of the fiscal year 1981. This report is an assessment of this contracting effort from the standpoint of cost and of quality control measures employed to ensure an acceptable product.

From abstract: The northern Black Hills bentonite mining district includes parts of Crook County, Wyo., Carter County, Mont., and Butte County, S. Dak. Within this district, many beds of bentonite occur interspersed with sedimentary strata of Cretaceous age that have an average total thickness of about 3,000 feet and consist chiefly of marine shale, marl, and argillaceous sandstone. The bentonite beds occur in formations ranging upward from the Newcastle sandstone to the lower part of the Mitten black shale member of the Pierre shale. Tertiary (?) and Quaternary deposits of gravel, sand, and silt are present on extensive terraces, and deposits of such materials also extend along stream courses in all parts of the district.

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: The chromite deposits of the central part of the Stillwater complex lie in a belt 9 miles long between the valleys of Boulder River and the West Fork of the Stillwater River in Sweet Grass County, Mont. The chromite occurs as layers near the middle part of the ultramafic zone in the lower part of the complex. The layers, originally horizontal, have been tilted so that they dip northeastwards at angles ranging from nearly horizontal to nearly vertical, and are cut by many cross faults, the largest with a horizontal offset of 3,000 feet. Investigations by the United States Geological Survey and the United States Bureau of Mines have shown that in this belt there are 5 sections ranging in length from 850 to 3,800 feet along the strike where the continuity and grade of the chromite can be reasonably inferred.

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.

This report studies the several aspects of the basalts in the Columbia River Basalt Group in the Spokane quadrangle, Washington, Idaho, and Montana.

Abstract: Anomalous radioactivity and uranium minerals have been found on the dumps of the Comet, Gray Eagle, and Silver Hill mines situated along the Comet-Gray Eagle shear zone. The shear zone is from 50 to 200 feet in width and has been traced 5 1/2 miles. The Gray Eagle mine is currently being reopened but no underground work, with the exception of a few shallow shafts and adits, has been done between the Gray Eagle and Comet mines. Because of the high U3 08 content of the samples from the Comet and Gray Eagle dumps, it is recommended that a minimum of four diamond drill holes totaling 3, 000 feet be drilled by AEC between the two mines to intersect the shear zone 300 to 500 feet below the surface. This drilling should be made contingent upon the results of the Gray Eagle exploration.

A report about phosphates found in the Permian Phosphoria formation of the Rocky Mountains. This area constitutes one of the worlds largest reserves of phosphate.

A report which includes 200,000 square miles in the southern part of the Williston basin of North Dakota, South Dakota, and Montana. The Devonian rocks consist mostly of marine carbonate, evaporite, and shale beds.

This report studies Devonian rocks in an approximately 200,000-square-mile area between Williston Basin, central Montana, and north-central Wyoming.

From abstract: Geologic settings are recognized in central and eastern Montana and in a few places in southwestern Montana that elsewhere are similar to the settings for the occurrence of uranium deposits. Several specific areas in Montana seem favorable for the occurrence of uranium.

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: "This report is a compilation and evaluation of water-quality measurements that have been made by the U.S. Geological Survey at two stations on the North Fork Flathead River." It contains a map, graphs, and tables.

A report explaining map symbols for the geologic map of the Northern and Western Flanks of the Black Hills, Wyoming and Montana.

From introduction: The purpose of this report is to provide estimates of 100-year flood discharges at selected sites in Glacier and Yellowstone National Parks. Estimates for streams with contributing drainage areas outside Glacier National Park were determined using only the contributing drainage area in the park.

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.

Abstract: Secondary minerals of the uranite group occur in dense quartz veins and in altered aplitic granite along and near the crest of the east-trending ridge about one mile west of Clancy, Montana. Brief examination suggests that the radioactive minerals are erratically distributed, but a more thorough study of the area will be made by the Geological Survey during the coming field season.

From introduction: The St. Regis-Superior area was studied during the summers of 1953 and 1954 as a part of geologic investigations by the U.S. Geologic Survey in and near the Coeur d'Alene district. The object of the present work was primarily threefold: to ascertain the main structural features in the area, with particular attention to the Osburn fault zone; to investigate the mineral deposits; and to determine the stratigraphic relations of the rocks.

From abstract: This report describes a rectangular area of about 2,600 square miles in Chouteau, Hill, and Liberty Counties, Mont., adjacent to the international boundary. The area is a portion of the Missouri Plateau, a section of the Great Plains province, and lies between the Highwood Mountains, Bearpaw Mountains, and Sweetgrass Hills, of north-central Montana. The southern part of the area is drained by the Missouri River and its tributary Marias River, but the northern part is drained by the Milk River. These streams are trenched in narrow valleys several hundred feet deep. The land surface between them is a rolling plain interrupted by very broad, shallow valleys that probably were eroded during the Pleistocene epoch by large streams whose courses were doubtless diverted from time to time by the continental glaciers. These valleys are now occupied only by very small creeks.

A report regarding the geology and mineralogy of the W. Wilson. Mine near Clancey, Jefferson County, Montana. This report concerns work done on behalf of the division of Raw Materials of the U.S. Atomic Energy Commission.

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

A report about the Lemhi Pass area in the Beaverhead Mountains, Lemhi County, Idaho, and Beaverhead County, Montana, which was undertaken to determine the area as a potential source of thorium.