"OpenGeoSci is a free, map-based discovery interface providing geographic searching for more than 300,000 maps, cross-sections, charts, tables, and other high-value content from GeoScienceWorld (GSW) publications. .... Search results can be filtered by journal, topical category, publication date, zooming in on the map, or an area filter."
"CGS is dedicated to the fulfillment of its mission to provide scientific products and services about the state's geology, seismology and mineral resources that affect the health, safety, and business interests of the people of California."
Google Advanced Search
This video describes the features of Google Advanced Search, which can help you focus your search results on exactly what you need.