In this photo, from around August 1964, we see that freestanding Sears and Davison's department stores are in operation. A mall that will connect the two is yet to be completed.
Photo from

The inline store section of COLUMBIA MALL was dedicated sometime around August of 1965. The fully-completed "dumbell plan" shopping hub consisted of a single level of retail. At the time of this site plan, it encompassed approximately 351,000 leasable square feet.