The incident that many historians credit with starting the Great Sioux War occurred near a Pony Express station at the north edge of Phelps County on the Platte River. Today the only evidence of what usually is referred to as the Plum Creek Massacre is a historical marker and small cemetery.

At the point where Plum Creek empties into the Platte River on the Dawson/Phelps county line, about 10 miles southeast of Lexington, Plum Creek Station on the Oregon Trail was established in 1859. The ranch or supply point was also a Pony Express Station and, in 1861, became a post office. What also was called the Post of Plum Creek was staffed as a “military post of substantial log construction … with a large garrison of soldiers” to protect travelers and settlers. As the Sioux and Cheyenne began staging raids along the trail in an attempt to halt the invasion of their hunting grounds, the site became a potential point for skirmishes because of its natural cover for attackers and the funnel-like area created along the trail by hills.

Thomas F. Morton and his 19-year-old wife, Nancy Jane Fletcher Morton, left their home in Sidney, Iowa, in July 1864 headed for Denver. On Aug. 6, the Mortons arrived at Plum Creek Station, where they joined 11 other mule-drawn wagons to form a train. The 12-wagon train consisted of 11 other men, perhaps a cook, Nancy Morton and Danny Marble, a boy of 7, 8 or possibly 13, whose father was one of the wagon drivers.