Fearless frontier scout and Indian fighter Kit Carson and his friends, Ape and Lopez, narrowly escape an attack by a tribe of gun-toting Shoshone Indians as they ride to Fort Bridger, the gateway to the Oregon Trail. After safely arriving at the fort, Kit is asked by wagon leader Paul Terry to guide his train south along the Oregon Trail to California. Kit at first refuses on the grounds that the trip is too dangerous, but when Terry and the wagons make arrangements to ride with Captain John Fremont and his cavalry troops, Kit reconsiders and agrees to lead the train. He soon finds himself in competition with Fremont for the leadership of the train as well as the attentions of Dolores Murphy, a young California beauty on her way to her father's hacienda in Monterey. Meanwhile, General Castro, the Mexican Governor General of California, arms the Indians in an effort to keep the Americans out of California. As the rivalry between Kit and Fremont mounts, Fremont insists upon leading his troops through a canyon, thus exposing them to the danger of ambush, while Kit insists upon leading the wagons along a safer route. As Fremont leads his men into the narrow pass, half the Indians dynamite the entrance, thus trapping the soldiers, while the other half of the tribe attacks the wagons. Kit blasts the entrance open in time to free the soldiers and rescue the wagons, and they continue on to Monterey. As Dolores and the others celebrate their safe passage at the Murphy hacienda, Castro plots the demise of the Americans. Kit discovers his plans when he sees some Mexican army wagons carrying guns to the general and learns of his plans to destroy the hacienda. As the Americans rally at the Murphy hacienda to raise the flag of the California Republic, Kit orchestrates the forces to defeat Castro. After successfully routing Castro and his troops, Kit is appointed colonel in the United States Army and bids Dolores farewell as he rides off to defend the California Republic.