Map showing lava flows in the southeast part of the Diacria Quadrangle of Mars

The Systematic mapping of lava flow units in the Tharsis region has been compiled into a series of 16 maps at 1:2,000,000 scale. This work provides information on the sources and areal extent of the lava flows, on their eruptive sequences and relative ages, and on relations between the flows and geologic structure in the largest, most active tectonic and volcanic province on Mars. Some of the maps were made from controlled Viking photomosaics published as quarter quadrangles in the Atlas of Mars Topographic Series (U.S. Geological Survey, 1979) and tied to the Viking control net. Where these photomosaics were not available, larger scale catalog photomosaics tied to the Mariner 9 control net were used. These maps were subsequently reduced to the 1:2,000,000 scale, but slight discrepencies may occur in places between features referred to coordinates on the two types of bases.