The device was reported at 10:46 a.m. in the 200 block of Channel Street, located just across McCovey Cove from the ballpark, and the all-clear was given some time before 3:20 p.m., police spokesman Carlos Manfredi said.
Construction crews at a site near Indiana and Mariposa streets apparently uncovered the device while sifting through dirt, and transported it to Channel Street, several blocks north, before notifying authorities, Manfredi said.
Manfredi said police want to discourage people from transporting a suspicious device that could be explosive.
"As a rule of thumb, if you see something that may go boom, stay away," he said.
The Police Department's bomb squad responded and determined the device was an old military-grade artillery shell. Police contacted Travis Air Force Base, which sent technicians to determine the exact nature of the device, Manfredi said.
The incident prompted street closures in the area and the evacuation of two nearby buildings, as well as residents living along the waterfront in houseboats, Manfredi said.