On: Grand Canyon Museum Had Buckets of Uranium Sitting...

[simonh]

Maybe that just means the ground is more radioactive than air?

[lightedman → simonh]

This is the correct answer. There're tons of microparticles of radioactive monzonite (and other radioactive minerals) in the dirt. And if you're near a granite body, you will show even higher levels of radiation.

Downvoters need to pick up a geology book.