Geologic map of science study area 4, Chasma Boreale Region of Mars
This map is one is a series of 1:500,000 scale maps initiated by the National Aeronautics and Space Administration to investigate Science Study Areas (selected area of scientific interest) on Mars (fig. 1). The Chasma Boreale region merits detailed geologic study because it contains parts of (1) the north polar ice cap, which is composed of water ice with lesser amounts of carbon dioxide; (2) the layered terrain that recorded climatic and atmospheric changes on Mars during the Amazonian Period; and (3) the enigmatic low-lying polygonal patterned terrain. The map was compiled on a composite of three 1:500,000-scale photomosaic bases (U.S. Geological Survey, 1986a, b, c), each of which is the summer scene of a two-sheet set that includes a spring scene. (Summer scenes, acquired when the north polar ice cap is smallest, show the greatest extent of underlying materials. However, spring scenes that show more detail in specific areas were also used.) Map units (including crater materials) and contacts are generally consistent with those of Howard and others (1982), Dial (1984), and Tanaka and Scott (1987) except where revised on the basis of higher resolution Viking images. Several Viking images were computer enhanced for our mapping.