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The Johnson Creek quadrangle is one of the 7} minute quadrangles which are being mapped for the Atomic Energy Commission in the Aspen Ridge--Dry Ridge area, southeastern Idaho, which contains most of the largest and best phosphate deposits in the western field. Geologic mapping is being continued in adjoining quadrangles and the mapping will serve as a basis for the calculation of reserves and the dif ferentia tion of areas suitable for mining.

Sandstone: hard, pale, yellowish-orange, thick-bedded Chert: hard, light-gray, thick-bedded chert interbedded with medium-hard, pale yellowish-orange, thick-bedded chert Sandstone and chert: medium-hard, light-gray, thick-bedded sandstone containing some iaterbeds of hard, light-gray chert 31 Sandstone and chert: medium-hard, brownish-gray, thick-bedded sandstone interbedded with hard, light-gray, thick-bedded chert 14 Sandstone: medium-hard, yellowish-brown, thick-bedded sandstone interbedded with hard, brownish-gray sandstone 10 Chert: medium-hard, dusky yellowish-orange, to medium-brown, thick-bedded Mudstone: medium-hard, light-gray to yellowish-brown, thick-bedded Sandstone: hard, light-gray to yellowish-brown, thick-bedded; lowermost 0.75 foot phosphatic 19 12 Member D Mudstone: phosphatic, soft, brownish-black, thin-bedded 15 Mndstone: soft, brownish-black to black, fissile 150 2OO 250 3OO 25 Phosphate rock: oolitic, soft, dark-brown, thin-bedded 22 14 Phosphate rock and mods too*: oolitic, medium-hard, brownish-gray, phosphate rock, interbedded with medium-hard, brownish-gray mudstone 12 Member C Sandstone: soft, dusky yellowish-orange, thick-bedded 41 Sandstone and chert: medium-hard, light brownish-grsy, massive sandstone interbedded with hard, yellowish-gray, massive chert 45 Dolomite: sandy, medium-hard, medium-to light-gray; contains lenses and nodules of chert Sandstone: soft, dusky yellow, thin-bedded; contains many lenses and nodules of chert 35 Chert: hard, medium-grny to yellowish-brown, thick-bedded; contains some interbeds of mudstone and sandstone Member B Mud atone: medium-hard, medium yellowish-brown, thin-bedded; contains several small lenses of oolitic phosphate rode 14 Phosphate rock and mudstone: soft, brownish-gray, oolitic phosphate rock interbedded with soft, pale yellowish-brown mudstone 20 Mudstone: medium-hard, medium yellowish-brown, thin-bedded Member A Mudstone: dolomitic, soft, light-gray, thin-bedded 349 10 Dolomite: medium-hard, pale yellowish-orange, thin-bedded; contains some interbedded cherty mudstone Quadrant formation Sandstone: medium-hard, light-gray, thin-bedded Figure 1. Generalized section of Phosphoria formation at Sheep Creek, Montana

Trace Elements Investigations Report 323 This preliminary report is distributed without editorial and technical review for conformity with official standards and nomen c la t ur e rt _ is__no t _f or _ pubreport concerns work done partly on behalf of the Division of Raw Materials of the Uo S. Atomic Energy Commission, and partly on behalf of the U. S, Bureau of Reclamation,,

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