SAN BERNARDINO COUNTY, Calif.—With their four-wheel-drive trucks hugging the mountainside, prospectors Ron Kliewer and Sean Hart dodge tire-puncturing rocks jutting out of the narrow and steep road to their inactive uranium and rare-earth mineral mines in the Mojave Desert.
Aside from a large uranium deposit, their square mile of mining claims is rich in 14 other critical minerals, including many rare-earth elements. The uranium there was first discovered more than 70 years ago, during the uranium boom after World War II and the dawn of the nuclear age.











