ANTIOCH -- Students at Deer Valley High have been released from school after being held off campus for more than an hour after the threat of an explosive device Monday afternoon.

Principal Ken Gardner said the school received an anonymous phone call around 1:45 p.m. warning of the threat of a device "in an undetermined location" on campus, then abruptly hanging up. He then sent out a robocall informing parents, as students were held on the athletic fields just off campus while the search was completed and all clear given.

"I'm very proud of our staff and our kids. The whole operation was very smooth," Gardner said, noting that the student body of 2,650 plus staff cleared out to the school's athletic fields in three minutes.

Parents also followed directions well, he said.

Antioch police were called to the school about the explosive threat, conducted a thorough search of the campus and did not find anything, Sgt. Tony Morefield said.

Gardner sent out a second robocall about 2:50 p.m. saying that the campus had been cleared and students released.

After-school events were not canceled and Tuesday will be a "normal day" on campus, Gardner said.

Antioch Superintendent Donald Gill pointed out that it's especially sad that the explosive scare comes one week after the bombing at Boston Marathon.

"Here you have this national tragedy, and somebody possibly trying to exploit it. It dishonors the victims in Boston and winds up turning the whole school upside down and disrupts student learning."

Contact Paul Burgarino at 925-779-7164. Follow him at Twitter.com/paulburgarino.