A legion of Mormon militiamen completed a massacre of at least 120 California-bound Arkansas pioneers at Mountain Meadow, Utah.

The Nauvoo Legion was a state-authorized militia of Nauvoo, Illinois, United States from February 4, 1841 until January 29, 1845. Its main function was the defense of Nauvoo and surrounding Latter Day Saint settlements, but it was also occasionally used as local law enforcement and paraded at ceremonies such as the laying of the cornerstone for the Nauvoo Temple. The Nauvoo Legion was unique among contemporary militias for its chain of command structure, its expanded functions of the court martial, and for operating at a city level.

The Mountain Meadows Massacre was a series of attacks during the Utah War that resulted in the mass murder of at least 120 members of the Baker–Fancher wagon train. The massacre occurred in the southern Utah Territory at Mountain Meadows, and was perpetrated by settlers from the Church of Jesus Christ of Latter-day Saints involved with the Utah Territorial Militia who recruited and were aided by some Southern Paiute Native Americans. The wagon train, made up mostly of immigrant families from Arkansas, was bound for California, traveling on the Old Spanish Trail that passed through the Territory.

California is a state in the Western United States that lies on the Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares an international border with the Mexican state of Baja California to the south. With almost 40 million residents across an area of 163,696 square miles (423,970 km²), it is the largest state by population and third-largest by area.

Arkansas is a landlocked state in the West South Central region of the Southern United States. It borders Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, Texas to the southwest, and Oklahoma to the west. Its name derives from the Osage language, and refers to their relatives, the Quapaw people. The state's diverse geography ranges from the mountainous regions of the Ozark and Ouachita Mountains, which make up the U.S. Interior Highlands, to the densely forested land in the south known as the Arkansas Timberlands, to the eastern lowlands along the Mississippi River and the Arkansas Delta.