A California man who was clearing out his father's Oro Valley home found a World War II "pineapple" grenade that he thought was inert.

He took the grenade - wrapped in a plastic bag - to the Oro Valley Main Police Station for disposal Thursday afternoon and was in for a surprise.

The grenade was determined to be active after it was inspected by members of the Pima County Regional Bomb Squad, said Lt. Chris Olson of the Oro Valley Police Department Field Services Division.

The Mk 2 defensive hand grenade was placed in a detonation container and taken to the Naranja Town Site, where it was blown up without incident, Olson said.

"This grenade was old, and it becomes unstable with age. The real danger with something like this is when you are moving it," Olson explained.

When the man arrived at the police station at 2:36 p.m., a sergeant followed explosive-ordnance protocol placed the grenade in a desert area west of the station. Officers then immediately evacuated the building and area around the town complex, and closed a portion of North La Cañada Drive.

Members of the county regional bomb squad arrived and inspected the grenade and determined it was live, and then transported it for destruction.

The man, whose name was not released, was moving his father to a nursing home, Olson explained. His father told him he kept the grenade as a "souvenir" and that it was inert.

The son did not want to take the grenade back with him to his home in California, and he knew that his father could not take it to the nursing home - so he figured that police officers could dispose of it.

Officers and bomb squad officers questioned the man, and no charges will be filed, Olson said.