Police gave the all-clear after investigating a bomb threat that forced Mt. San Antonio College in Walnut to cancel classes and evacuate students Thursday morning, creating a traffic nightmare for those trying to leave campus.
The threat indicated that something would take place on campus at 2:45 p.m., prompting school officials to issue an emergency alert.
Students and staff were asked to "calmly leave the campus," which officials say will remain closed until at least 4:30 p.m.
Images from the scene showed a long queue of drivers attempting to make their way off campus.
A lock down at nearby Walnut High School was lifted about 1:30 p.m.