Where was Fort Clenendin?
In the wild west of the Imagination is one answer.
However, Col. Stuart Valois, the commander of Fort Clenendin, quotes a reply from his superior, a general stationed at Fort Wallace, that the Arapaho war chief Hanu would never dare attack Fort Clendendin because it was too close to other forts like Wallace, Dodge, Hays, Bascom, and Garland.
And those are the names of real forts in the real west.
Fort Wallace (c. 1865-1882) was in Wallace Country, Kansas, at coordinates 38°54′18″N 101°33′34″W
Fort Dodge (1865-1882) was near Dodge City, Kansas and at coordinates 37°43′50″N 99°56′5″W.
Fort Hays (1865-1889) was near Hays City, Kansas, at coordinates 38°51′42″N 99°20′32″W
Fort Bascom (1863-1870) in New Mexico was at coordinates Lat: 35.3178303 Long: -103.7032995
Fort Garland (1858-1883) was in Costillo County, Colorado, at coordinates 37°25′46″N 105°26′7″W
(it was strange that they didn't mention Fort Larned [1859-1878] and Fort Harker [1866-1872], between Fort Dodge and Fort Hays. Fort Larned was in Pawnee County, Kansas at 38°10′59″N 99°13′05″W. Fort Harker was at Kanopolis, Kansas at 38°42′35″N 98°9′25″W, but it was abandoned in 1872 before the date of Chuka.)
Fort Wallace was 1.483 degrees north of Fort Garland, and so about 102.3 miles north of it. Fort Hays was about 218 miles east of Fort Garland. The road distance from Fort Garland to Fort Hays is about 403.7 miles, longer than as the crow flies.
Dialog gives the impression that Fort Wallace was the closest fort to Fort Clenendin.
Sergeant "Slim" says he hasn't tried to desert, because it is 59 miles north to Granada and 63 miles south to Stone Creek. Granada, Colorado is east of Fort Garland, at coordinates 38°3′53″N 102°18′40″W,. 59 miles south of Granada would be at about 38 degrees 13 minutes north, in Colorado. 63 miles south of that should be near route 40 in the Texas Panhandle, near Amarillo & Tascosa.
Added 10-8/9-24. Actually 59 miles south of Granada should be at about 37 degrees 12.45 minutes north and about 102 degrees 18.6 minutes west. 63 miles south of there should be about 36 degrees 14 minutes north. So Fort Clenenden should be south of Walsh, Colorado, which is at 37°23′9.99″N 102°16′47.76″W, and the fictional Stone Creek should be near Stratford, Texas which is at 36°20′15″N 102°04′34″W.
So I guess the fictional fort Clenendin would would have been about 130 miles from Fort Wallace and slightly farther from Fort Doge.