The incident was reported just after 1 p.m. at a Chevron station located at 1325 California Ave., police said.
Ventura was with a number of acquaintances in the parking lot when the suspect confronted him and opened fire. Emergency personnel gave aid but Ventura died at the scene, according to police.
A description of the shooting suspect was not immediately available. Police are asking anyone with information about the case to call Detective Erik Severe at (925) 252-4836.