The crash occurred at the intersection of Canyon Ridge and Summerhill drives around 7:15 a.m.
CHP said the bus driver, identified as Jeania White, 43, of Lake Elsinore, misjudged the speed of an approaching Honda and made an unsafe turn in the intersection.
The Honda was unable to stop and collided with the left front of the bus. The school bus came to rest in the middle of the intersection with the Honda lodged under the front of the bus.
Firefighters freed the 18-year-old driver, identified as Ryan Geiger, from the wreckage. He was transported to Inland Valley Medical Center with major injuries.
White was later transported to the hospital due to feeling ill.
No students were hurt.
Investigators do not believe drugs or alcohol played a role in the crash.