Check out the little Carnagie Library...Lots of Boulder History and flyers and maps you can use to find things you might be interested in! Very interesting history on the early gold mining areas just West of town.
If you are interested in the history of Boulder, and historic sites, you can take Banjo Billy's bus tour. It is a sort of "boulder-weird" style bus tour that covers unique Boulder history and trivia. You will see the bus driving around town, you can't miss the custom painted school bus.