Students at La Jolla, Lincoln, San Ysidro and Scripps Ranch high schools were secured in their classrooms for part of the morning Tuesday as a precaution due to unfounded bomb threats issued in quick succession by unknown perpetrators.
The campuses received the menacing telephone calls over a roughly 15-minute period starting about 10:15 a.m., according to school district officials.
Administrators instituted the so-called shelter-in-place measures, which are less intensive than a full-scale lockdown, while police carried out sweeps of the buildings and grounds at each site.
At no point did the threats seem credible to authorities, and no hazards were found, according to officials with San Diego Unified School District, whose campuses include those in La Jolla, Lincoln Park and Scripps Ranch. Campus police issued all-clear announcements at each of those three schools by midday, SDUSD spokeswoman Linda Zintz said.
San Diego police, meanwhile, went through the San Ysidro campus and declared it safe shortly before 11 a.m., said Manny Rubio, an information officer for Sweetwater Union High School District.
Normal operations had resumed at all four campuses by early afternoon.