SAN MARCOS, Texas (KXAN) – A man trespassing in the Lower Purgatory Creek Natural Area stumbled upon what authorities believed was an old explosive charge, The City of San Marcos explained Thursday.

The man was wandering the closed park between 8 and 9 Thursday morning and found several wires sticking out of rubble about 100 yards from The Wonder World extension pass. He called San Marcos police who called the Austin Police Department bomb squad for assistance.

It was determined there may still have been an active explosive attached to the wires that should have been used during construction of the nearby dam. The dam was built several decades ago.

Members of the bomb squad detonated the explosive around 1 p.m. San Marcos officials said it was a small blast and posed no threat.

Lower Purgatory Creek Natural Area remains closed while City crews and volunteers repair the extensive damage caused by last year’s flooding. Upper Purgatory Natural Area and Prospect Park, which are adjacent to the closed park, are open to the public.