The field work for this report was begun in April, 1880, and concluded in March, 1881. In the spring of 1880 the Census of the Mineral Industries West of the Rocky Mountains was placed in my charge in addition to my duties as geologist, and occupied much of my time both during the period of field work in the Washoe District and since.

Nevada↗

USGS1875

Preliminary report upon a reconnaissance through southern and southeastern Nevada, made in 1869

By authority from headquarters Military Division of the Pacific, Lieut. George M. Wheeler, United States Engineers, will proceed with his civil assistants and three enlisted men to either Camps Halleck or Ruby, Nevada, and having been joined by Lieut. D.W. Lockwood, United States Engineers, now en route via Fort Churchill, will there organize a party, to consist of two-non-commissioned officers and twenty-three enlisted men, (cavalry, or infantry mounted,) such drivers, packers, and guides as may be required; equip them with the necessary, full, and complete outfit, as far as the resources of the posts will enable him so to do; after which he will proceed, via the White Pine district, to make a thorough and careful reconnaissance of the district of country to the south and east of White Pine, extending thereto from the White Pine or Grant district, of obtaining correct data for a military map of the country, and for the selection of the site or sites for such military post or posts to cover the mining country south and east of White Pine from hostile Indians, as may be required. Such explorations and examinations as may will be made in reference to the physical geography of the country, its resources in wood, water, agricultural or mineral productions. The character, habits, and numbers of Indian tribes, and their dispositions toward settlers and miners, will be subjects for investigations.

Nevada↗

USGSDate not supplied

Relations between geological structure and aeromagnetic anomalies in central Nevada

An aeromagnetic survey of a 6000-km 2 area in central Nevada has been complied by the U.S. Geological Survey. An interpretation of the aeromagnetic data is developed to establish relations between near-surface geological features and structure extending to intermediate depths in the crust. A three-dimensional distribution of magnetized material is described which would reproduce approximately the observed aeromagnetic anomalies. Anomaly sources extend from the surface to depths exceeding 15 km and require values of magnetic moment per unit volume averaging more than 2000 × 10 −6 (cgs). Magnetic anomaly lineations were analyzed by two methods. The first involves digital fan filtering and subsequent autocovariance computations. This method is sensitive to amplitude of linear anomalies, and indicated a dominant north-northwest trend with approximately 80 percent of the anomaly trend power in an azimuth range of northwest to northeast. The second method involves preparation of rosettes from measured lengths and azimuths of lineations indicated by noses and flexures on the contoured map. This method is not sensitive to anomaly amplitude. The dominant N. 10°E. trend determined in this way is indicative of the effect of near-surface geological structure on the magnetic field. The dominant north-northwest-trending zone of magnetic anomalies is located along an alinement of windows through the Roberts Mountains thrust fault. This suggests that elongate doming of the Paleozoic sedimentary rocks associated with the thrust may be related to emplacement of magnetic anomaly source material, and implies that this has been a zone of recurring tectonic activity since late Paleozoic time. Analysis of stresses possibly associated with forceful injection of magnetic anomaly sources and possible shear deformation along this north-northwest-trending zone suggests that these factors may have had a secondary influence on azimuths of high-angle faults and dikes.

Nevada↗