Our "Top Picks" for geology databases are a good place to start. Use the Tabs (left) for additional resources. Tips:
1) Mix and match your subject (fluvial systems, isotope geochemistry, mineralization, etc.) with the names of: rock units (Fountain Formation, Pierre Shale); structures (Paradox Basin, Beartooth Uplift); locations (Jefferson County, Golden quadrangle); time periods (Upper Cretaceous, Precambrian).
2) Are some of your findings "old"? Field studies, mapping, observation, and lab analyses can still be valuable after decades.
3) Does your subject cross disciplines? Consider searching the literature of chemistry, engineering, environmental science and others.
4) Having trouble finding a specific publication? Check with a librarian--Some works (conference proceedings, field guidebooks, etc.) are quirky and can be difficult to discover.
(Big Thompson Mesa, UT. NASA Earth Observatory, 2009.)