Search USGS⌕ Search

Geology topics

Robert C. Jachens

Publications and source records attributed to Robert C. Jachens.

67 records · Page 4Linked to original sources
USGS1987

Mineral resources of the Fort Piute Wilderness Study Area, San Bernardino County, California

The Fort Piute Wilderness Study Area (CDCA-267) is in northeastern San Bernardino County, California, near the boundary between California and Nevada. Mineral surveys were requested for 31,371 acres of the Fort Piute Wilderness Study Area. In this report the area studied is referred to as "the study area". Examination of mines and prospects in the area was accomplished by the U.S. Bureau of Mines in 1981 and 1982. Field investigations of the area were carried out by the U.S. Geological Survey in 1983 and 1985. No mines or prospects, few mining claims, and no identified resources are located within the wilderness study area. Moderate and low potential for gold resources appears limited to outcrops of gneiss and granite exposed along the eastern side of the Piute Range. Available information indicates that there is no potential for energy resources, including oil and gas, uranium, or geothermal, in the study area.

California↗
USGS1986

Mineral resources of the Castle Peaks Wilderness Study Area, San Bernardino County, California

The Castle Peaks Wilderness Study Area (CDCA266) comprises approximately 45,000 acres in the northern New York Mountains, San Bernardino County, California. At the request of the Bureau of Land Management, 39,303 acres of the wilderness study area were studied. The area was investigated during 1982-1985 using combined geologic, geochemical, and geophysical methods. are considered preliminarily suitable for wilderness deignation. There are no mineral reserves or identified resources in the study area. Fluorspar, occurring in sparse veins, has moderate resource potential, as do silver and lead in fault zones, and gold and silver in sparse, high-grade veins and fault breccia. Each area of moderate resource potential encompasses less than one square mile. These same commodities have low resource potential in similar occurrences throughout much of the study area. In addition, there is low resource potential for gold in placer deposits, uranium in altered breccia and gouge, and rare-earth elements in pegmatite dikes. There is no resource potential for oil and gas resources over most of the study area, but the potential is unknown along its western margin. In this report, the area studied is referred to"the wilderness study area", or simply "the study area."

California↗
USGS1986

Mineral Resources of the Warm Springs Wilderness Study Area, Mohave County, Arizona

At the request of the U.S. Bureau of Land Management, approximately 113,500 acres of the Warm Springs Wilderness Study Area (AZ-020-028/029) were evaluated for mineral resources and mineral resource potential. In this report, the area studied is referred to as the 'wilderness study area' or 'study area'; any reference to the Warm Springs Wilderness Study Area refers only to that part of the wilderness study area for which a mineral survey was requested. This study area is located in west-central Arizona. The U.S. Geological Survey and the U.S. Bureau of Mines conducted geological, geochemical, and geophysical surveys to appraise the identified mineral resources (known) and assess the mineral resource potential (undiscovered) of the study area. fieldwork for this report was carried out largely in 1986-1989. There is a 1-million short ton indicated subeconomic resource of clinoptilolite-mordenite zeolite and an additional inferred resource of 2 million short tons near McHeffy Butte, approximately 2 miles west of the study area. A perlite deposit in the southeast corner of the study area contains an inferred subeconomic resource totaling 13 million short tons. An inferred subeconomic resource of gold in 225 short tons of quartz having a grade of 0.01 8 troy ounces per short ton is present at the Cook mine, 0.5 miles west of the study area. The northwestern part of the Warm Springs Wilderness Study Area has high mineral resource potential for gold and silver. The south-central part of the study area has one area of moderate and one area north of this south-central part has low mineral resource potential for gold and silver in and near Warm Springs Canyon; the mineral resource potential for gold is also moderate in three small areas in the southern part and one area in the northeastern part of the study area. The mineral resource potential for zeolite is high for the area surrounding the McHeffy Butte prospect and for one area in the southern part of the study area. Two areas inside the south and southeast boundaries of the study area have high mineral resource potential for perlite. The potential for ka: olinite resources is moderate in two areas in the southern part of the study area. The southern part of the study area has low resource potential for perlite and zeolite. Geothermal energy resource potential of the study area is low. The study area has no resource potential for oil and gas.

Bulletin↗
USGS1985

A new isostatic residual gravity map of the conterminous United States

In order to display more clearly the gravity anomalies caused by bodies of geologic interest in the crust, a new colored isostatic residual gravity map of the conterminous United States has been prepared using the gravity data set compiled for the Gravity Anomaly Map of the United States (SEG, 1982). The isostatic residual map is based on an Airy-Heiskanen model of local compensation, with the surface load requiring compensation being defined by 5-minute topographic and bathymetric data sets. Because topography-related anomalies have been removed to first approximation, the resulting isostatic residual map highlights density contrasts associated with geologic bodies in the crust. For example, the 2000 km-long gravity high that follows the Appalachian orogenic belt is delineated along its entire length without the topographic overprint characteristic of Bouguer maps. For purposes of displaying gravity anomalies caused by shallow bodies of geologic significance, the nature of the isostatic model and the values of its parameters are of lesser importance than the application of an isostatic correction of some sort. Most isostatic models will result in residual maps which appear very similar in their main patterns and features. Anomalies on isostatic residual gravity maps should not be casually interpreted in terms of "undercompensation" or "overcompensation" because large amplitude anomalies can be produced by crustal bodies in complete local isostatic equilibrium.

Conference Paper↗
USGS1983

Map showing aeromagnetic interpretation of the Golden Trout Wilderness, Tulare and Inyo counties, California

The Golden Trout Wilderness covers 457 mi 2 in the rugged forested part of the southern Sierra Nevada. It is bounded on the east by Owens Valley, on the north by Sequoia National Park, and on the west and south by U.S. Forest Service multiple-use lands. The east side of the area is accesible from U.S. Highway 395, while the remainder is reached by state, county, and Forest Service roads from the San Joaquin Valley.

California↗
USGS1983

Geophysical maps and interpretations of the Domeland Wilderness and contiguous Roadless Areas, Kern and Tulare counties, California

Geophysical maps were compiled and constructed from gravity and aeromagnetic surveys of the study area in order to assist the geologic mapping and the mineral resource assessment of the Domeland Wilderness and contiguous roadless areas. The isostatic residual gravity map (fig. 1) primarily reflects lateral density variations within the upper crust beneath the region studied. The aeromagnetic map reflects the distribution of magnetization in the underlying rocks. Because different rock types are often characterized by different densities and magnetic properties, the geophysical maps can be used to extend the geologic mapping into areas covered by surficial deposits and to help determine the subsurface locations and attitudes of contacts between rock units with contrasting properties.

California↗
USGS1983

Precision gravity networks at Lassen Peak and Mount Shasta, California

Reoccupiable precision gravity networks for the purpose of monitoring volcanic activity were established in the vicinity of Lassen Peak and Mt. Shasta. Base-line measurements were made during the summer of 1981, nearly coincident in time with other base-line geodetic measurements. The gravity surveys yielded gravity values at network stations relative to local bases with typical uncertainties of 0.007 mGal (1 computed standard error).

Open-File Report↗
USGS1983

Precision gravity network for monitoring the Lassen geothermal system, Northern California

A precision gravity network consisting of approximately 50 stations was established to monitor the Lassen geothermal system. The network was surveyed during the summer of 1982 and tied to a similar network established in 1981. Measurements yielded relative gravity values at the network stations with average uncertainties of 0.007 mGal (1 computed standard error).

Open-File Report↗
USGS1978

Results and interpretation of geophysical studies near the Picacho Fault, south-central Arizona

Earth fissuring attributed to ground-water withdrawal occurs throughout south-central Arizona. A large zone of active fissures is located near Picacho, Arizona on the eastern rim of a large subsidence bowl. The main fissure has been named the Picacho fault. During February and March 1977, approximately 6.5 km of seismic-refraction lines were run across the Picacho fault to investigate subsurface conditions down to the crystalline basement. In addition, two lines of close-spaced gravity stations were made across the fault. The gross geologic features inferred from the gravity data agree with the seismic interpretations. Six layers were interpreted from the seismic refraction data: three layers of unconsolidated alluvium, two of denser rock of varying porosity, and the basement rock. Three significant basement faults were identified. These faults appear to lie almost directly beneath the surface fissures. Abrupt slope changes in the alluvial layers and an abrupt velocity change in the denser compacted sediments seem to be related spatially to the surface fissures. In addition there are lateral velocity differences within the basement fault blocks. In the overlying sediments a facies change in a 3.0 km/sec layer is suggested by the abrupt lateral velocity increase from 3.0 km/sec to 3.7 km/sec. This apparent facies change may in fact represent a fault plane extending upwards from the westernmost basement fault. This fault plane may even extend farther into the unconsolidated overlying sediments, inferred from basinward increases in slope, subtle basinward decreases in velocity, and a basinward elevation decrease in the top of the zone of saturation.

Open-File Report↗
USGS1977

Mineral resources of the Tracy Arm-Fords Terror Wilderness Study Area and vicinity, Alaska

The Wilderness Study Area consists of about 322,300 hectares (1,250 square miles or 796,400 acres) on the southwest side of the Coast Range in southeastern Alaska about 72 km (45 miles) southeast of Juneau, Alaska (fig. 1). An additional 142,800 hectares (550 square miles or 352,900 acres) lying in part between the study area and the International Boundary and in part contiguous to the southwest of the study area were studied because of their importance to the evaluation of the study area itself. Unless otherwise specified, the term Study Area as used in this report includes both the formally designated study area and these contiguous areas. The general area is one of spectacular scenery, with fiords, forests, glacier-covered peaks to 2,470 m (8,095 feet) high, tidewater glaciers, icebergs, and some broad river valleys. No roads or maintained trails or permanent residents are present, and access is only by specially arranged water or air transport. Present human use of the area is related to recreation or mineral-resource exploration.

Alaska↗