I've been using the Fort Griffin setting myself from Dog House Rules (makers of Sidewinder: Recoiled d20 Wild West).
I've mixed OGL WW/Sidewinder and been running a game in this area for a bit now.
Dog House Rules free maps/info
http://www.doghouserules.net/recoiled/download.html
My game, Fort Griffin 1871
http://online-roleplaying.com/forums/forumdisplay.php?f=622