The crash happened a little after 5:30 p.m. on the interstate near Orland, a small city about 100 miles north of Sacramento.
The bus was one of two that the admissions office at Humboldt State University had chartered to bring prospective students from Southern California to tour the Arcata campus, Humboldt's Vice President of Administrative Affairs Joyce Lopes said.
The bus was owned by Silverado Stages, a tour bus company based in San Luis Obisbo. The company said in a statement on its website Thursday night that it was assisting authorities in gathering information.
"Our top priority is making sure that the injured are being cared for," the company said.
Humboldt State President Rollin Richmond issued a statement on the school's website. "Our hearts go out to those who have been affected, and we are here to support them, and their families, in any way possible," Richmond said.
The students came from a number of Southern California high schools and Humboldt spokesman Simon Chabel said the college was working to confirm where in Southern California all the were from.
Los Angeles Unified School District Superintendent John Deasy said late Thursday night that an unknown number of students from Robert F. Kennedy Community Schools were on the trip and possibly students from Manual Arts Senior High School, Banning High School and Augustus F. Hawkins High School. He did not know whether they were on the bus involved in the crash. District officials were headed up to the crash site Friday, said spokeswoman Gayle Pollard-Terry.
A high school senior from Alliance Renee & Meyer Luskin Academy High School in Los Angeles said she and a few of her classmates who were accepted to the university were invited to go on the tour.
Sabrina Garcia said the tour began Thursday, with buses taking students in Southern California on the ride to the campus for a three-day stay there. She said she decided to postpone the tour because she had a school project to complete.