Grand Canyon National Park, Arizona - A sign warns hikers away from an old mine on Horseshoe Mesa due to radiation concerns.

- Image ID: D65RRD
Jim West / Alamy Stock Photo
Image ID: D65RRD
Grand Canyon National Park, Arizona - A sign warns hikers away from an old mine on Horseshoe Mesa due to radiation concerns. Though the miners were after copper, it was often mixed with uranium.
Location: Grand Canyon National Park, Arizona