Dreadnought by Cherie Priest
Mercy Lynch is a recently-widowed nurse working in a Confederate hospital during a strangely-elongated American Civil War when she gets news that her long-missing father is injured and possibly dying in the distant state of Washington. Mercy immediately leaves the hospital and journeys West aboard the locomotive Dreadnought, surrounded by all kinds of characters: a Texas Ranger, a spy, hostile Indian warriors, Union soldiers, Confederate soldiers, Mexican bandits, ladies of easy virtue, and a huge army of zombies.
Steampunk fun in the altered American West : it doesn't get better than this! Don't look for historical accuracy here--the history of this America has taken a sharp turn away from our reality, and into a very interesting place of its own. Dreadnought is the sequel to this author's Boneshaker (another steampunk story, set in gold-rush Seattle), but stands alone beautifully.
Recommended for readers ages 14 to adult. Some romance but no on-page sex (the ladies of pleasure go off-stage for business purposes), some drugs (including the drugs that turn soldiers into zombies!), some wartime violence, plus a few bloody scenes of amputation in a Civil War-era hospital.