SPOKANE, Wash. (AP) -- Officials at the Lake Roosevelt National Recreation Area say they found explosive materials on two occasions this week.
Tubes containing explosive material were found on Tuesday and Thursday within the boundaries of the recreation area.
Each time the bomb squad from Spokane destroyed the material.
The National Park Service said Friday the explosives are used in mining and excavations.
The Park Service says the tubes cannot explode on their own, and do not pose a significant risk to the public.
Park rangers are working with the sheriff's offices for Ferry County and Stevens County to determine where the tubes came from.