Authorities lifted a lockdown order at a sprawling U.S. Army Reserve facility in Northern California after not finding anything suspicious Tuesday following reports of a possible gunman.

The Alameda County sheriff's office said the training center was searched and that the reports had been "unfounded."

There were initial reports of a possible shooter at the Camp Parks Reserve Forces Training Area, but no one was spotted, Alameda County sheriff's Sgt. Ray Kelly said.

Law enforcement officials from a variety of agencies responded to the facility in Dublin, about 35 miles east of San Francisco.

Officials say that all Dublin schools where students are attending summer school and other programs were put under a shelter-in-place order from the superintendent that was later lifted.

The Camp Parks Reserve Forces Training Area is a semi-active mobilization and training center for Army Reserve personnel.

Ray Pauly, whose window overlooks the facility, said he didn't hear any gunshots but saw authorities lined up and down the street outside his home.

"We heard a huge siren say, 'Everyone go into your house,'" Pauly said.