The Crossings: A Terrifying Novel of the Old West, Paperback

It's the Arizona Territory. The year, 1848. The year the Mexican War ended. Fate and blazing pistols have just thrown together reporter and part-time drunk Marion T. Bell and the very nearly legendary John Charles Hart, mustanger and scout, in the Little Fanny Saloon in the town of Gable's Ferry. A rough place in a lawless era.
About to become a hell of a lot more so one night when Hart, Bell and the easy-going giant Mother Knuckles stumble upon Elena, a fierce, young, badly wounded Mexican woman near the banks of the Colorado. She tells them about the torment she and her sister have endured at the hands of las hermanas de lupo, the deadly Valenzura Sisters and their henchman, the deserter Paddy Ryan, at the well-manned slave-camp across the river aptly called Garanta del Diablo--Mouth of the Devil.
It's just three hundred years since Cortez. Only three hundred years since the Old Gods of Mexico were in their full and fearsome flower. Tezcatlipoca, god of the moon and the night. Tlazolteotl, Eater of Filth. Xipe, Lord of the Flayed. Blood for rain. Blood for bounty. For many, like the Valenzura Sisters, they have never died.
And Elena's sister's still there.