The Probability Broach (North American Confederacy #1)
Author: L. Neil Smith
Desc: Denver detective Win Bear on the trail of a murderer discovers much more than a killer. He accidentally stumbles upon the probability broach a portal to a myriad of worlds--some wildly different from others disconcertingly similar to our own. Win finds himself transported to an alternate Earth where Congress is in Colorado everyone carries a gun there are gorillas in the Senate and public services are controlled by private businesses.