USGS Thesaurus (and Related Vocabularies)
The USGS Thesaurus is a broad, shallow formal thesaurus intended to help people outside USGS find scientific information resources without having to know the organizational structure of USGS itself.
Controlled Vocabularies Expressed as RDF-XML using SKOS:
Natural Sciences Vocabularies & Ontologies
Physical Sciences Vocabularies & Ontologies
Formalization(s) of Geologic Time [2, 3]
Ontology of Volcano System and Volcanic Hazards Assessment 
Ontology of Fractures 
- Raskin, R. G. & Pan, M. J. (2005) Knowledge Representation in the Semantic Web for Earth and Environmental Terminology (SWEET). Computers & Geosciences 31, 1119-1125.
- Cox, S. J. D. & Richard, S. M. (2005) A formal model for the geologic time scale and global stratotype section and point, compatible with geospatial information transfer standards. Geosphere 1(3), 119-137.
- Perrin, M. & Mastella, L. S., (2011) Morel, O. & Lorenzatti, A. Geological Time Formalization: an improved formal model for describing time successions and their correlation. Earth Science Informatics 4(2), 81-96.
- Tripathi, A. & Babaie, H. A. (2008) Developing a modular hydrogeology ontology by extending the SWEET upper-level ontologies. Computers & Geosciences 34, 1022-1033.
- Fauziati, S. & Watanabe, K. (2010) Ontology of Volcano System and Volcanic Hazards Assessment. International Journal of Geoinformatics 6(4), 49-62.
- Zhong, J., Aydina, A., & McGuinness, D. (2009) Ontology of Fractures. Journal of Structural Geology 31, 251-259.