Edward S. Ellis - In the Pecos Country

Edward Sylvester Ellis was a major American author during the era of inexpensive fiction of the nineteenth century (dime novels). Because he wrote under dozens of pseudonyms, as well as under his own name, it is virtually impossible to know exactly how many books he wrote, but it is believed to be in the hundreds. He specialized in boys' stories, inspirational biography, and history for both children and adults. (From FictionDB.com)
This is a western, set in the Pecos River valley in the late 19th century, post Civil War era.