Wagon trains

Caravans of covered wagons
Caravans of wagons
Covered wagon caravans
Emigrant trains
Trains, Wagon
Wagon caravans

Work cat.: William Henry Jackson Papers Digital Library Project, 2001 (Wagon train crossing the Platte Bridge)
Encyc. Americana, 2001 (Wagon trains, caravans of covered wagons that served as the principal means for settlement and supply of the far-western United States before the coming of the railroads ... Wagon caravans carried settlers and essential goods westward over the Santa Fe, Oregon, and other trails.)
New Encyc. Britannica, 1997: v. 12, p. 450 (Wagon train, caravan of wagons, wagon-train transportation moved westward ... wagon-train migration are more widely known and written about than wagon freighting, which also played an essential role in an expending America.)
Encyc. of the American West, 1997: pp. 451-454 (Wagon trains; Emigrant trains)