A popular guided cave in Sequoia/Kings Canyon National Park has been shut down after crews found what is believed to be 1930s vintage explosives next to the underground trail.

Park Officials report that over 50,000 visitors a year make the long winding drive to take the guided tour of Crystal Cave. On Friday, crews installing a new lighting system in Crystal Cave found wires coming out of three different holes in the rock right next to a trail. All employees and visitors were evacuated and Crystal Cave closed to the public.

Park officials report that of the three spots, only one is likely to contain live explosives left over from Civilian Conservation Corp construction crews that built the trail through the cave in 1939.

This week park staff will try to remotely remove the wires and any attached explosives, but they also may have to detonate the material in place. Park Officials say that there is a distinct possibility that the explosives used to develop the cave included nitro glycerin, which becomes unstable over time.

The hope is to avoid explosions, but that could be the safest way to get rid of the explosives. In preparation for this possibility park staff will install temporary blasting mats and blankets to protect cave formations and features.

If all goes according to plan, Park Service Staff hopes to re-open Crystal Cave by this weekend.