This map comes from the U.S. Geological Survey and state Department of Natural Resources database. The map units are identified in the metadata file there, but their ages can be determined in many cases by the capital letter in the symbols on the map key, which is included in two larger versions I have made of this map. The 1500x1700 pixel version weighs 1.3 MB and the 3100x3600 pixel version is 2.9 MB. Both have fully legible textin fact, the larger one should print better than the original GIF.
More Georgia resources on About.com:
Georgia Geography, State Symbols & Facts
Georgia National Parks
Southeast U.S. Travel