A radiometric reconnaissance of the areas adjacent to the principal highways and secondary roads of south-central Alaska was carried out during the summer of 1947. The investigation included the examination of nine gold-placer workings, five gold lodes, a gypsum mine, and a copper prospect. Nearly all types of rock cropping out in the highway belt were tested. No significant amounts of radioactive material were found.

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The highest equivalent-uranium co'ntent found in the sedimentary rocks on the upper Porcupine River, northeastern Alaska, is 0.005 percent. Rhyolitic dikes associated with a granitic intrusive a few miles north of the Porcupine, along the international boundary, contain about 0.006 percent equivalent uranium, which is attributed to small amounts of disseminated radioactive accessory minerals. The granite also is slightly radioactive.