These are from the FGDC Digital Cartographic Standard for Geologic Map Symbolization (PostScript Implementation) http://pubs.usgs.gov/tm/2006/11A02/
  
The complete document and all symbols is called "FGDCgeostdTM11A2_web_all.pdf"

Files in USGS Pattern Pages
"FGDCgeostdTM11A2_A-37-01.ai"
were downloaded in CS2.EPS format and converted to .ai. These are pages from the full document that have patterns (swatches).

Swatches have been stripped out to be used directly in Ai in the "USGS_Swatches" folder. 

Read instructions to see how to use them.
  
Suggested citation
  U.S. Geological Survey, 2006, FGDC Digital Cartographic 
       Standard for Geologic Map Symbolization (PostScript 
       Implementation): U.S. Geological Survey Techniques 
       and Methods 11-A2 
       [http://pubs.usgs.gov/tm/2006/11A02/].

