Young Bill Hickok (1940) on Netflix

Plot summary

A foreign agent works to bring California under his control while the Civil War keeps the East occupied. Morrell and his Overland Raiders take the horses the stagecoach and Pony Express relay stations depend on, cutting the lines to the East. Bill Hickok is posted to one of those stations to keep its ponies out of the raiders' hands. Horse traders Calamity Jane and Gabby Whitaker arrive there alongside their Indian helpers. Louise Mason, Bill's former fiancée, also turns up; the pair had broken off their engagement because she favored the Confederacy and he did not, and she wants to mend matters. Marshal Evans, who oversees the communication lines, asks Bill to carry a shipment of gold east for the Federal war effort.