Eleven soldiers attempt to hold a river crossing in the middle of the desert

The Colorado River's most vital point for American settlement is the ferryboat at Yuma Crossing. When the gold rush begins, a gang of white outlaws seizes the ferry from the local Yuma tribesmen, who have operated the crossing for decades. The US Army rousts the outlaws, but the high command decides to keep the crossing rather than return it to the Yuma. No one considers how badly the Yumas want the ferry back.

Left in command of the ferry is Lieutenant Thomas Sweeny, a one-armed Irishman who wins the dangerous assignment by bringing charges against an alcoholic major. Hundreds of miles from reinforcements, he occupies the position with a ten-man force, limited supplies, and no way to call for help. In the distance, four hundred Yuma prepare for battle, intent on reclaiming what once was theirs.