A State Patrol spokesman says the trooper and a cadet were parked on the shoulder of I-5 monitoring traffic when the speeding driver hit a patch of standing water and lost control, plowing into the trooper's patrol car from behind.
The trooper is being checked for back soreness. The cadet was not hurt, nor was the offending driver.
Trooper Guy Gill of the State Patrol says alcohol and drugs were not a factor in the crash.
Some lanes of the freeway were closed for a time after the crash, creating a temporary backup at the scene.