San Antone Ambush (1949)

"THRILLS! ACTION! SUSPENSE! ADVENTURE! When A Framed Union Cavalry Officer Ana A Texas Bandit Fight Side By Side For Law and Order!"

Just after the Civil War a Texan and his men are fighting a ruthless Commissioner and his excessive taxes. After a Lieutenant is falsely accused of a pay wagon massacre by the Commissioner's men, he deserts the Army and tries to clear himself. At first he belives the Texan was behind the massacre but then learns it was the Commissioner and joins the Texan in his fight.