King of the Bad Men of Deadwood #nn (1950)

"Dunc Blackburn" follows a notorious outlaw who guards the treacherous Deadwood coach route in 1877, using his double-barreled shotgun to stop gold shipments from reaching their destination. A woman named Jane infiltrates the operation by posing as a cavalry recruit, earning Blackburn's trust while secretly working to undermine his criminal enterprise. The story culminates in a cavalry charge against Blackburn's forces at Gary's Bend in the Black Hills, where Jane participates in combat while maintaining her cover as a soldier.