Police arrested freshman Mark Christopher Woods after they found two partially assembled pipe bombs in his dorm room.
Assistant Vice-Chancellor Lisa Lapin says police also found explosive materials.
"I took a look at it and there were a lot of plastic bags full of powder and they filled about five milk crates."
Lapin says Woods violated campus policy.
"You cannot have any kind of explosive material, pyrotechnic material in student housing. Even a chemistry major wouldn’t have reason to have any of this kind of material in their room. I mean experiments are done in the laboratory."
Woods is being held in the Yolo County jail. Police say there was no imminent danger of explosions and no evidence of terrorism.
Students were allowed back into the dorms around noon yesterday.