On July 20, 1976, Viking 1 made the first successful landing on Mars in Chryse Planitia, a plains-covered basin in the northern hemisphere. Viking orbiter pictures reveal more surface detail of the area and show the basin to be more complex than was seen on Mariner 9 images. The plains consist of areas with smooth and relatively uniform surfaces with prominent lunarlike mare ridges, mesas and plateaus, surfaces that appear to be 'etched,' fields of knobs, low shields that may be volcanic, and vast areas that have been subjected to channel-forming processes. At least two sets of channels, originating from distant sources, terminate in Chryse Planitia. The four major units of the basin are basal hilly and cratered terrain, plateau material which can be divided into upper and lower units, lower smooth plains, and upper smooth plains. There is no evidence for the origin of the basin. Deposition of the plateau-forming material to the east followed the period of bombardment, and since that time the history of the basin includes eruptions of flood lavas, channel formation, and deposition with at least two channel-forming events. The later history of the basin includes possible local volcanic events, etching, and acolian activity.