Blood Ruby by Kiernan Kelly

Finnian is an Irish folk healer, a witch who specializes in healing magic. He’s new to America and is going west to seek his fortune in a place rumored to be steeped in magic — a town called Ruby Gulch, deep in the New Mexico Territory. When he meets Ishago, an injured Navajo on the trail, their lives become inexorably entwined. They risk their hearts and lives to steal a magic stone from a sleeping dragon, and in the process set events in motion that may destroy them all.