A campus lockdown at San Clemente High School has been lifted after authorities searched the school early Thursday after a threat was posted on a social media app.
The bomb threat was posted on Yik Yak, a social media site on which users can post anonymous comments.
The campus was placed on lockdown shortly after the 9 a.m. posting and was lifted at 1 p.m.
Students and staff were told to shelter in place while a sweep of the campus was conducted, said Lt. Jeff Hallock, spokesman for the Orange County Sheriff's Department.
Members of the sheriff's bomb squad, which used dogs during the search, found no evidence of an explosive.
A school resource officer discovered the threat while investigating a separate incident on Yik Yak, Hallock said.
Authorities said they are attempting to identify to author of the bomb threat.
But the app, with the tagline "no profiles, no passwords, it's all anonymous," may make it difficult to determine who posted the threat, authorities said.