Authorities diverted vehicles off the freeway near the Magnolia Avenue exit.
The northbound lanes of the freeway remained closed for about three hours during the investigation. Caltrans said the lanes were reopened shortly after 9 p.m.
A coroner was on the scene because the person who jumped did not survive.
No further information was immediately released.
Authorities urged drivers to use the 57 Freeway to avoid the congestion.