Viking 1 was launched on August 20, 1975 and arrived at Mars on June 19, 1976. The first month of orbit was devoted to imaging the surface to find appropriate landing sites for the Viking Landers. On July 20, 1976 the Viking 1 Lander separated from the Orbiter and touched down at Chryse Planitia (22.48° N, 49.97° W planetographic, 1.5 km below the datum (6.1 mbar) elevation). Viking 2 was launched September 9, 1975 and entered Mars orbit on August 7, 1976. The Viking 2 Lander touched down at Utopia Planitia (47.97° N, 225.74° W, 3 km below the datum elevation) on September 3, 1976.
Man, that brings back some memories. My father was working for NASA Langley during the time of Viking, and he was sent out to Pasadena for two weeks to troubleshoot the imager for V1. I have a photo taken by the actual Viking 1 camera of the JPL parking lot. My father also says that somewhere out there is a photo consisting of a landscape with three images of Carl Sagan, after he stood still for one part of the panoramic image, then ran over to the middle of the shot and stood still, then ran over to the far end of the view. The camera panned so slowly, taking one vertical strip at a time, that he was able to show up three times in the same shot.