Ambush valley

the long version

"Chet Byrnes has his hands full taking care of his family and running his ranching operation in Arizona Territory. But he still takes his responsibilities as a deputy U.S. marshal very seriously. Bandits have been crossing the border, cutting a bloody swath of mayhem--stealing horses, robbing banks, and murdering innocent folk--then high-tailing it back to safety in Mexico. The chief U.S. marshal asks Chet to lead a secret task force to stop the raids and round up the border bandits--dead or alive. But the bandits fight back--putting a five-hundred-dollar bounty on Chet's head. Now he's got bushwhackers to deal with, and when he's led into an ambush, it's kill or be killed in a life-or-death showdown..."-- From back cover.