In a mid-1960s-vintage aerial, we see recent modifications to the shopping complex. A Best's Apparel store has filled in the original center court. Moreover, an extended South Wing is anchored by a shiny new Penneys.
Photo from Malls of America Blogspot 

Graphic from Alstores Realty Corporation

The south end of the mall, as it appeared following the mid-'60s expansion. The south portal of a service tunnel may be seen.
Photo from Meredith L. Clausen / Permission for use granted

By the time of a circa-1965 site plan, the entire structure (not just the central shopping concourse) is known as NORTHGATE MALL. The complex was still open-air, albeit with the "Sky Shield" semi-enclosure. It would be reconfigured as a fully-enclosed facility in 1974.