File:America's Highways 1776–1976 - page 325b.jpg

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English: This is a circa 1935 electrical resistivity test along the George Washington Memorial Parkway in Virginia. An electric current is passed through steel rods to measure ground resistance. This geophysical method is used to locate subsurface rock formations.
Date
Source https://en.wikisource.org/wiki/Page:America%27s_Highways_1776%E2%80%931976.djvu/331
Author Federal Highway Administration

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Public domain This image is a work of a United States Department of Transportation employee, taken or made as part of that person's official duties. As a work of the U.S. federal government, the image is in the public domain.

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current18:50, 3 January 2023Thumbnail for version as of 18:50, 3 January 20231,035 × 707 (627 KB)Sp1nd01Uploaded a work by Federal Highway Administration from https://en.wikisource.org/wiki/Page:America%27s_Highways_1776%E2%80%931976.djvu/331 with UploadWizard

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