Geography.

In 1851 the wagon train leaves Missouri for California. When they pass near the Red River, the border of Texas, Dunstan decides to head south to Texas.

If the wagon train was planning to use the Santa Fe Trail to Santa Fe, New Mexico, and then go south along the Rio Grande to southern New Mexico, and then west into southern Arizona and cross the Colorado River into southern California, they would pass about one or two hundred miles from the closest point where the Red River was the border of Texas.

Unless the wagon master got lost very, very badly. So if the Indians didn't kill everyone they would all die in a Donner Party like disaster anyway.

If the wagon train used the more popular Oregon-California trail they would be going a few hundred miles north of the Santa Fe Trail and thus even farther from the Red River border.

When Dunstan gets into Texas he heads south looking for a good place for a ranch. And he finally finds a good place for a ranch at the Rio Grande river.

The closest distance between the Red River border of Texas and the Rio Grande border of Texas is about 250 miles, I think, and the distance can get as high as twice that in some places.

According to the movies, there was basically no occupation in Texas except for cattle ranching until oil was discovered. According to the movies nobody farmed in Texas and there were no cotton plantations whose rich owners plunged Texas into the Civil War against the best interests of the majority of Texans.

So if Texas was all cattle ranching country according to the movies, why did Tom Dunstan travel hundreds of miles into Texas before he found a good enough place for a ranch?

If Texas was only good for cattle ranching according to western movies, and if large areas of Texas weren't even good for that according to Red River, Texas would seen like a rather useless place in the movies.

The movie Texas might make one tend to agree with General Sherman when he said if he owned both Hell and Texas he wold live in Hell and rent out Texas.

And now those viewers who complain that they can't understand the distances involved in the proposed alternate cattle drive routes may understand who is responsible for their confusion, and guess what kind of grades Howard Hawks, Borden Chase, and Charles Schnee got in geography.