I didn't see this posted anywhere here.. Sorry if I missed it.
A VERY interesting general history of Colorado and tales of several lost mines/treasures. Geology of each location is explained in fascinating detail. I give it FIVE STARS!!!
Other states featured are Arizona, California, New Mexico, Nevada, and Utah.
http://www.thegeozone.com/treasure/colorado/index.jsp
Don't forget to always do your homework to make sure that you're not breaking any laws before you go swinging a detector or pick.
Boogie