RDR is set in 1911, pre-dating San Andreas by 81 years. My theory is that there are links to GTA San Andreas, but needs alot of research so could you help?
1. Coot's Chapels link to Las Brujas, Bone County?
2.Col. Henry Bolt, 66th Cavalry charge towards Las Barancas in 1842. Is there a reference in RDR?
3. Is Fort Carson the same Fort Mercer. Jake describes the soldiers as having gone north to fight indians or gone in search of gold..... or was it the charge of '42?
A number of locations in the desert could of been used in RDR. Rockstar could well of made reference to San Andreas, though despite being an older game and the 81 year gap would not be entirely accurate. but similarities would be noticeable.
I haven't played San Andreas, but just going by what you've written I'll note that there is a location in RDR called Barranca (similar name to Las Barancas). Also, note that there is a real Fort Carson, though it is a modern Army post built in 1942.