Police say he was planning to attack students and staff at Crafton Hills College.
"It's shocking to say the least. I had no idea honestly," said student Brandon Kimbler.
Police arrested 30-year-old Stanley Roring on Tuesday.
Police say Roring posted a message on his Facebook page threatening violence. Campus police were alerted to it by someone who had access to the page.
"We were very fortunate that someone reported the postings that were put on the web and that our police department and the county sheriff's immediately investigated and resolved the issue," said Crafton Hills College President Gloria Macias Harrison
It's unclear why the alleged threat was made or who the intended targets may have been.
Investigators with the San Bernardino County Sheriff's Department say they recovered evidence at Roring's home, but they would not say what that was.
"We do believe that the threats were legitimate," said Cindy Bachman of the San Bernardino County Sheriff's Department.
School administrators alerted staff to the incident, and some students were told by their instructors during class. Those who knew about the threat say they were horrified.
"All I heard was that he was going to shoot up this place. He was after some teacher," said Brittany Dominick of Redlands.
Roring is being held on $50,000 bail for making criminal threats. He also faces disciplinary action by the college, which may include expulsion.