Airr04:
Almost every state has a department of mines, minerals or geology. Most of them have issued very interesting publications that are accurate and inexpensive. Most sell maps, as well.
Some of the best from a "hobby perspective" came out in the 1930's, when state and the Federal government government were teaching people to pan for gold during The Great Depression.
Many of the Western states' publications have been reprinted by private individuals. My point out is the information is accessible and generally not expensive.
What state are you interested in exploring? Perhaps I could offer you a few suggestions.
Good luck to all,
~The Old Bookaroo