There's a new site for research for us prospectors called Land Matters, it's Non-Profit Educational Organization website primarily for prospectors and other land users, this site was created by Brian Cole and Leigh Johnson, with much help from MinerDiggins Adventures, who many may know as Clay and Ruby, who have been for years been producing mapping and mining claims programs for prospectors.
The site has been posted on other gold prospecting forums but I haven't seen it posted here, it's free to use, many many hours have been put into this site and more to come, there are many different maps and map layers (geology, land status, minerals, mining, topos, etc.), articles, resources, and a searchable library for 8 states at this time and more states are coming as requested by end users as well as the entire USA and other parts of the world, it takes a little time and work to add each state but several more states are in the works at the time I'm posting this and will be added in the order they have been requested by end users, if you have a request please request it at the website or I can relay it to them.
As mentioned it a non-profit project created out of the passion of what we do and many, many hours have been put into it's creation which isn't finished by a long shot, but they do accept donations if you are so inclined.
www.mylandmatters.org/
P.S. If Administrators feel this is worthy, please pin it so it's easy to find, I have already requested and have had them add South Carolina and North Carolina..., Colorado, Georgia and Alabama was added prior to my request, Virginia, Tennessee and other eastern states have been requested by me and are in the works as I type this.