Lucky Luke arrives to captured the Daltons when Piotr, the leader of the immigrants from the wagon train, welcomes Lucky Luke and later on exposes their problem to them: They have 80 days to go to California and to take possession of their land, if not the developer, a man named Crook, having put 12 caravans in danger so that they do not arrive in California with his partner Bartleby, keeps the money paid in advance without the sale being made.

Among the other immigrants headed for California include a Chinese chef couple, a teacher with unruly children named Miss Littletown, a trash-talking driver for a pack of mules that transport the Daltons and a barber among others.

With the next bridge being far away for 6 days to travel, Miss Littletown suggested to turn the wagons into hot air balloons and fly over the canyon.

The Daltons flee with their stock into the abandoned gold mine, resulting in a chase in the form of a roller coaster ride between the settlers, Lucky Luke, Rantanplan and Crook.

Suddenly, as Crook makes his escape, a mega explosion was caused by the dynamite now fetched by Rantanplan, destroying the loot the Daltons stole and allows the settlers to discover gold under the sold lands.