The pilot, who's from Orange, had to touch down after the 1968 Piper airplane ran out of gas. Four people were onboard. No one was injured.
Dispatchers say there was some traffic on the road when the plane landed but the pilot managed to avoid the vehicles.
A pickup truck driving by after the landing did clip one wing.
Traffic delays resulted, lasting longer than usual due to the unusual roadside sight.
"The airplane was able to be pushed to the right shoulder and will remain on the right shoulder until it is determined how to safely remove it," said a California Highway Patrol officer.
The southbound I-15 offramp at El Norte Parkway was expected to remain closed through the Monday afternoon commute as mechanics worked to remove the aircraft from the area, according to Caltrans.
City News Service contributed to this report.