In the mid-1800s, horse traders Travis Blue and Sandy Owens lead a herd of horses they have captured into the southwestern town of Crystal City, hoping to sell the animals for a good profit. After talking the town's unsuspecting marshal into buying one of their wild horses, Travis and Sandy are approached by two Mormons, the irreverent Jonathan Wiggs and the pious Adam Perkins. Upon learning that the traders are familiar with the region, Wiggs tries to hire them as wagon masters for his small band of Mormon settlers, who are headed for the San Juan Valley in Utah. Anxious to gamble in town, the men at first decline the offer, but later change their minds and join the Mormons, who have been forced to leave Crystal City because of their religion. Not far into the desert, the Mormon group comes across a troupe of stranded medicine show performers, who ran out of water after being driven out of Crystal City and have been drinking their own "elixir" for three days. Although Adam disapproves of the intoxicated troupe--leader Dr. A. Locksley Hall and assistants Floretty "Florey" Phyffe, Mr. Peachtree and young, pretty Denver--Wiggs sympathizes with their plight. Describing their chance meeting with the California-bound troupe as an act of God, Wiggs persuades Adam to allow the performers to ride along with the group. As the emigrants push farther into the desert, their water supplies begin to dwindle, and Travis orders everyone, including the feisty Denver, to conserve. Finally, however, Sandy locates a river, and the thirsty group rushes for relief. That night, a dance is held in camp, giving Travis a chance to romance Denver, while Sandy woos Adam's daughter Prudence. The festivities are interrupted by the arrival of the Clegg family, five fugitive outlaws led by coldblooded killer Uncle Shiloh. Although the smooth-talking Shiloh, who was shot in the shoulder during a murderous holdup, claims that he and his "boys"--brothers Luke, Reese, Jesse and Floyd-- are cowboys, Travis, Sandy and Wiggs know their true identity. To protect the group, however, Travis, Sandy and Wiggs decide to allow the outlaws to travel with them. When Shiloh learns that there is a "doctor" in the group, he orders Hall at gunpoint to remove the bullet from his shoulder. Later, while searching for an alternate route, Travis is pursued by a band of Navajo braves. The Indians chase Travis back to the group, but upon learning that the emigrants are Mormon, their chief invites them all to their camp that night. During the "squaw dance," an Indian woman accuses Reese of attacking her, and Wiggs immediately orders the outlaw to be flogged by his followers. Although Shiloh resents the punishment, he permits it to go on to avoid trouble. Soon after, at the California cutoff, the medicine show troupe says goodbye to the Mormons. Before they get very far, however, Travis proposes to Denver, but is rejected. The troupe's wagon is then stopped by Shiloh, who orders them at gunpoint to return to the wagon train, where they can be watched. Determined to avoid capture by the marshal's posse, Shiloh announces to the entire wagon train that he and his boys will continue on with them until they reach the San Juan Valley. As anticipated, the marshal and his posse come to question the train, and the outlaws hide in various wagons, holding guns to the backs of the Mormons until the posse leaves. That night, Wiggs, Sandy and Travis discuss the final leg of their journey, which involves traversing steep, rocky terrain. Sandy, who has gotten a gun from Prudence's young brother, then argues with Travis about dealing with the outlaws, but the gun-shy Travis declines to act until the Mormons are safely delivered. The next day, the men dig a fresh trail over the rocks, and all of the wagons except the heavy grain wagon make the crossing. To avenge Reese's flogging, Shiloh, who has overheard Wiggs say that their grain is "more valuable than gold," orders the elder to drive the grain wagon, whose horses Floyd intends to scare into a deadly run. Before Floyd carries out his orders, however, Sandy draws his gun and shoots him. Travis shoots and kills the remaining brothers, then outdraws the sneaky Shiloh. With their enemies dead, the Mormons continue to the beautiful San Juan Valley, where Sandy finally kisses Prudence, and Travis reunites with Denver.