From introduction: The Bear Valley district is situated in southwestern Idaho, in the drainage of the Middle Fork of the Salmon River (see fig. 1). The placer deposits were drilled by the U. S. Bureau of Mines in 1951 and 1952 to determine their content of monazite and "radioactive black minerals" (here referred to loosely as "radioactive blacks"). The purpose of the study outlined here was to provide a geologic background for an understanding of the origin and distribution of the placer minerals.

Photograph of the Series 90-S Mobile Spar. According to author Eric Orlemann, "the Mobile Spar was a diesel-electric transporter equipped with a folding 130-foot guy wire tower." It was built for hauling lumber up steep slopes. Only one unit was built and sold to a lumber company in McCall, Idaho.