The Lowman mill site is in north-central Boise County, Idaho, about 73 miles northeast of the City of Boise. It is in the Boise National Forest one-half mile northeast of the village of Lowman (on State Road 21).

The Idaho batholith igneous complex extends about 300 miles N-S by 50 to 100 miles E-W in southwestern Idaho. It is comprised mainly of large intrusive bodies of medium to coarse-grained granite, quartz monzonite, and granodiorite. Pegmatite dikes are common in the granites. In this terrain, stream gravels and higher bench gravels contain placer deposits composed primarily of resistant, heavy-mineral grains (black sand) that were released from the batholithic rocks by weathering (decomposition and erosion). Placer deposits that formed in valleys that drain weathered quartz-monzonite outcrops contain a higher percentage of thorium-bearing minerals. These placers were mined for monazite (a thorium-bearing mineral) in the period 1903-1910 and again in the late 1940s. The thoria content of Idaho monazite is reported to be somewhat lower than other available commercial monazite concentrate.