At about 10:20 a.m., a person walking a dog reported seeing the device in the Presidio area at Inspiration Point off of Arguello Boulevard.
U.S. Park Police responded to the device, deemed it to be suspicious and notified San Francisco police.
According to Williams, authorities cleared out the surrounding area as they investigated the device.
The bomb squad determined the device was a World War I mortar and it was rendered safe at about 2:45 p.m.
