"Fort Massacre"
In "Fort Massacre", 2 February 1959, the fictional Fort Anderson is in danger of being captured by hostile Indians which would result in the garrison being massacred.
How fictional is Fort Anderson? While en route to Fort Laramie with an army payroll Jim Hardie's stagecoach reaches Fort Anderson in Apache territory. Fort Anderson is supposed to be near Fort Laramie yet also in Apache Territory.
Fort Laramie, Wyoming. Coordinates 42°12′33″N 104°32′9.1″W
https://en.wikipedia.org/wiki/Apache#/media/File:Apachean_ca.18-century.png
I guess that's as fictional as any western fort could get.