Randolph Air Force Base is visible as two white strips northeast of the city. The base’s streets were laid out in a series of concentric circles, with the runways along the east and west sides. This pattern can be seen in the series of Landsat images. Randolph Field was dedicated on June 20, 1930, so there is not much change to see to the base itself. What changes is the amount of residential buildup surrounding the base, development creeping in from the southwest and spilling over the north side of the base.
Street patterns in residential areas are clearer in some images than in others. As trees in these neighborhoods mature, they begin to cover the streets, so you will see this progression in these images.