Officials at the Grand Canyon are investigating whether anyone was exposed to radiation at unsafe levels while samples of uranium ore sat in plastic buckets in a research building.
National Park Service spokeswoman Vanessa Lacayo says the three five-gallon buckets have been removed from the building that houses the park’s archives and artefacts.
About 550 people tour the collections every year, mostly by appointment.
Ms Lacayo said the agency is working with Arizona health and workplace safety officials on the investigation.
The Arizona Republic cited the Grand Canyon’s safety director in saying the park did not warn workers or the public of the potential harm that existed for years.
Uranium can be harmful depending on the amount, how people interact with it and the exposure time.