The mules and Jules Brown sit on the DeLorean.
A mule is an animal that is the offspring of a male donkey and a female horse. As mules are stronger than horses of the equivalent size, they are often used for pulling or carrying heavy items.
On March 3, 1850, Marty McFly, Jules Brown, and Verne Brown disguised the DeLorean time machine as a covered wagon.
When Daniel Clayton and Martha O'Brien's wagon train arrived, they loaned let them join the wagon train, and lent them two mules.