Geophysical investigations in the Humboldt River valley near Winnemucca, Nevada
AuthorWilson, George M.
Geological Sciences and Engineering
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Magnetic and gravimetric surveys were conducted in a portion of the Humboldt River Valley near Winnemucca, Nevada, as a preliminary phase of a geophysical program authorized under the State of Nevada’s Humboldt River Research Project. The primary purpose of these surveys was to determine the possibility of delineating buried basalt flows using magnetic methods and to obtain the depth of basin sediments using gravity data. Subsequently, the gravity investigation was extended to determine whether a subsurface barrier exists across the outlet of the Humboldt River drainage in the vicinity of Rose Creek. The magnetometric surveys show that buried basalt flows can be delineated, that qualitative depth calculations are possible, and that in a detailed survey, it is often possible to correlate subsurface structure with surface geology. A detailed magnetometer survey of the Kern Ranch suggests that the exposed basalts in those localities do not dip continuously beneath the alluvium and the ’’broken rock" described by the driller's log of the Kern well may not be basalt. On the basis of gravity data, the basin sediments in Grass Valley are estimated to be over 4600 feet thick, and the sediments in the Rose Creek area at least 1200 feet thick. Variations in thickness of the valley fill, as determined by combined magnetic and gravimetric surveys, reflect the structure and configuration of the basement in the areas mentioned above. The gravity survey south of Rose Creek gives strong evidence for a subsurface barrier across the Humboldt River drainage. A low may exist in the center of the barrier, but more geophysical data is necessary for a positive interpretation.
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Humboldt River Valley
State of Nevada Humboldt River Research Project
delineating buried basalt flows
qualitative depth calculations