Rock type maps for the North America Tapestry of Time and Terrain map.
Four smaller maps show the distribution of four principal types of rock: sedimentary, volcanic, plutonic and metamorphic.
Metamorphic rock
Plutonic rock
Sedimentary rock
Volcanic rock
Home: http://pubs.usgs.gov/imap/i2781/
Image: http://pubs.usgs.gov/imap/i2781/i2781_c_low.pdf 144 dpi, encoded to 72 dpi JPEG, compressed slightly to fit within Wikipedia 2MB limit.
Source: English Wikipedia, original upload 15 April 2005 by SEWilco
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