A helpful statewide atlas for California is Warren A. Beck, Historical Atlas of California (Norman, Oklahoma: University of Oklahoma Press, 1974. (Family History Library book 979.4 E3b; fiche 6054102).
The Family History Library has a selection of maps of the gold regions and mining districts, ghost towns, railways, and topographic features. Large map collections from pioneer times to the present are also at each of the University of California campuses (including Berkeley, Davis, Los Angeles, Riverside, San Diego, Santa Barbara, and Santa Cruz) and the fourteen campuses of California State College.
United States Census Bureau State and County Map. This map will allow you to zoom in on any state or county in the United States and read the names of all of the neighboring counties.
Printable maps are also available from the National Atlas of the United States -- http://nationalatlas.gov/printable.html