The two grenades found Saturday buried in a Petaluma man’s front yard date back to the World War II era, the sheriff’s office said Monday.

The grenades were found when the homeowner was doing some landscaping, trimming shrubs, and found them buried beneath the bush, said Petaluma Police Sgt. Jeremy Walsh.

When police arrived about 2 p.m., they called the sheriff’s office for help.

The devices were identified by the Sonoma County Sheriff’s Office Explosive Ordinance Disposal team as Mk 2 grenades.

“The devices were live at one point, and (later) probably filled with concrete,” Walsh said.

The Petaluma department issued an alert Saturday notifying residents about police activity in the 200 block of McNear Circle when they learned of the discovery, Walsh said.

“We took it as a found property type of thing,” he said. “It wasn’t really suspicious on any level.” Walsh said the sheriff’s office planned to detonate the devices.

During the WWII era, military restrictions weren’t as strict, and often soldiers would bring back grenades as souvenirs from the war, which then find their ways into attics, novelty shops, and apparently, front yards.

The grenades found by the Petaluma homeowner Saturday were introduced in 1918, and are also known as “pineapple hand grenades,” according to the website militaryfactory.com.

They were phased out in the 1960s.

You can reach Staff Writer Christi Warren at 707-521-5205 or christi.warren@pressdemocrat.com. On Twitter @SeaWarren.