The Purgatoire River drains an area of 3,449 square miles (8,930 km2), mostly in Colorado but a small percentage of the watershed is in New Mexico.

It empties into the John Martin Reservoir and the Arkansas River near the town of Las Animas at an elevation of 3,852 ft (1,174 m).

Periods of zero water flow have been recorded near Thatcher, Colorado and the Pinon Canyon Maneuver Site, a large (in area) U.S. army base on the west side of the river.

Valverde named it "Rio de las Ánimas," meaning "River of the Spirits," as a warning to subsequent explorers of the dangers of crossing the nearby Ratón Pass.

By the end of the 18th-century Spanish traders believed it to be "Rio de las Ánimas en Purgatorio," or "River of the Souls in Purgatory," after a supposed massacre that occurred on its banks.

They related their translation to members of the Stephen H. Long expedition in 1820 [11] who renamed it "Purgatory Creek" by removing all references to souls.

Mountain Men had difficulty pronouncing the French translation and called it "Picatoire," while Anglophone settlers during the Colorado Gold Rush anglicized it to "Picketwire," despite the river having no relation to any fence.

[14] Depending on the language spoken, the river had five different names - Ánimas, Purgatorio, Purgatoire, Purgatory, and Picketwire - by the end of the 19th century.

[20] Coal mining began at Starkville in 1865 and soon became the major economic activity in the hilly and mountainous country west of Trinidad.

[21] By the early 1900s the coal mines in the Purgatoire watershed employed thousands of men, most of them born in southern and eastern Europe.

Labor disputes, unsafe working conditions, and diminishing demand for coal caused most of the mines to shut down after World War I (1914-1918).

[27] The site is located on public land of the Comanche National Grassland, along the Purgatoire River south of La Junta in Otero County.

It is also mentioned as the Purgatory in the Pulitzer Prize winning book Lonesome Dove by Larry McMurtry, as the place where the renegade Blue Duck goes into hiding.