What is The Fictional Date of Duel in the Sun?

The correct answer is sometime in the imaginary wild west era of novels, movies and TV shows.

A narrator during the overture says Duel in the Sun happens in Texas in the 1880s.

But we can make estimates of when it might happen if it happened in real history.

In "Where is Spanish Bit?" it is shown that the ranch of Spanish Bit and the nearby town of "Paradise Flats, the Paradise of the Pecos" should be in the Pecos River Valley in west Texas. Since Newt says he will ride to El Paso, the city in the westernmost point of Texas, Paradise Flats and Spanish Bit should be on the westernmost edge of the Pecos River Valley to make such a ride as reasonable as possible.

While Newt is away, a railroad lays track up to the east fence of Spanish Bit, having legally obtained the right of way from the State of Texas. Senator McCanles calls hundreds of ranch hands to the fence to shoot down any rail workers who cross the fence, but the US cavalry arrives to protect the workers from being murdered.

Three railroads laid track in west Texas in the early 1880s.

The Southern Pacific from California laid tracks across Arizona and New Mexico and reached El Paso on May 19, 1881. The Galveston, Harrisburg and San Antonio Railroad laid tracks west from San Antonio not far north of the Rio Grande, while the Texas and Pacific Railway laid tracks west from Fort Worth and passed not far south of the New Mexico border.

On December 15, 1881 the Southern Pacific Line met the Texas and Pacific line at Sierra Blanca, Hudspeth county, Texas and continued to the Southeast, meeting the Galveston, Harrisburg and San Antonio Railroad at a point three miles west of the Pecos River near Langtry, Texas, completing the second transcontinental railroad, on January 12, 1883.

Spanish Bit could be near Langtry, with the Galveston, Harrisburg, and San Antonio Railroad laying track from the east to the east fence of the ranch. But then Newt would have ride a couple of hundred miles to El Paso (unless he got on the Central Pacific train at their nearest station).

The Texas and Pacific Railway, laying track close to the New Mexico border, reached Toyah, Texas, not too far from the hypothetical location of Spanish Bit, on September 12, 1881, and linked up with the Southern Pacific at Sierra Blanca on December 15, 1881.

The railroad from the east that reaches Spanish Bit should be either the Texas and Pacific in 1881 or the Galvaston, Harrisburg, and San Antonio sometime in 1882 or early 1883.

https://tshaonline.org/handbook/online/articles/eqt08

http://www.ttarchive.com/Library/Articles/Texas-Pacific_Oxteams-to-Eagles.html

In the movie the railroad seems to be the fictional(?) Texas and South Western Railroad.

https://obscuretrainmovies.wordpress.com/2017/04/01/duel-in-the-sun-1946/

The many flags of the large cavalry force that protects the railroad workers indicate later dates.

The cavalry have many company guidons, fork tailed flags, red above and white below, with the regimental number "3" in white above and the company letter in red below. This pattern of guidon has been used by the US cavalry since 1885.

http://www.crwflags.com/fotw/flags/us%5Ecav.html

The two colors or standards seem to be 36 inches high by 48 inches long. The national standard has a pattern like the United States flag, while the regimental standard has the United states coat of arms on a yellow field.

https://obscuretrainmovies.wordpress.com/2017/04/01/duel-in-the-sun-1946/

https://obscuretrainmovies.files.wordpress.com/2017/04/duel012.jpg

The use of a pair of standards seems to date back to 1895. Before that the US cavalry only used a regimental standard, blue, 2 feet 3 inches high by 2 feet 5 inches long, with the US coat of arms.

The Third Cavalry was stationed in New Mexico & Arizona from 1866 to 1871, in Wyoming in 1871 to 1882, fighting in the Great Sioux War, in Arizona from 1882 to 1885, in Texas from 1885 to 1893, and moved to Kansas and Oklahoma in 1893.

So the railroad data indicates the date is 1881 or 1882, the presence of the Third Cavalry indicates 1885 to 1893, and the cavalry flags indicate the date is in or after 1895.

But western movies almost always use the wrong cavalry flags, often put cavalry regiments where they weren't at the time, and often have railroad service where and when there wasn't any. So in the wild west of the imagination, the only clue to the date of Duel in the Sun is the narrator saying it is in the 1880s.