Article in June 1921 Canning Age notes their use of trucks to bring the crop to the cannery. Brought peas in from Mt. Eden, San Leandro. Also cites that sending fruit by rail meant stopping picking by 2:30 to get the crop to the railhead. With the trucks, they could be picking til almost 5:00.
My father remembers that the Del Monte San Leandro was still canning some grades of fruit with H.G. Prince labels in the 1940's when he held summer jobs there.
See photos of employees from Oakland Museum.