Geologist Jay Temple kept his audience interested and asking questions about rare earth minerals as he led them through a discussion of minerals analysis and geologic mapping in Custer and Fremont Counties during a presentation last month. Temple is a field geologist and is working with the Colorado Geological Survey (CGS), a state agency situated within the Colorado School of Mines, on a two-county mapping project and examination of critical rare-earth minerals, which is jointly funded by the U.S. Geological Survey (USGS) and CGS. The study includes aeromagnetic surveys, which passively measure subtle variations in the Earth’s magnetic field from the air, thus “aeromagnetic anomalies.” Differences in the magnetization of rocks from the surface to deep in the Earth cause aeromagnetic anomalies. You may have…