Day of Rage.
(Book)

It was there for the taking: $75,000 in gold bullion, the combined payrollsof three productive gold mines, just waiting to be stolen from under the noses of a bickering sheriff and city marshal. Billy Ray Gilmore and his band of kill-crazy outlaws have a plan to do it, too-that is, until Sixkiller comes to town. Hiding his badge to conceal his identity as a U.S. marshal, Sixkiller goes undercover to smoke out the culprits before they strike. But in this town full of four-legged rattlesnakes, deadly surprises lurk behind every saloon door. To keep from being bitten, Sixkiller will have to lay a few traps of his own. Lucky for him, what this town lacks in law, it makes up for guns--and dynamite.