The map on the wall of Micah's office shows the pre-Civil War borders of the New Mexico Territory, which also encompassed Arizona. The territory had been split during the war.
Grandpa is too young: The series in Season 5 is set circa 1882. John Anderson plays Sam, who is Mark's maternal grandfather. Anderson was 1 year younger than Chuck Connors. As of the air date, Connors was age 41, Johnny Crawford was 16, and Anderson was 40. Since Lucas and Mark had been in North Fork for about 5 years at this point, this made Mark about 11 when they arrived- he would have been born post-civil war circa 1866. In the best-case scenario if his mother gave birth at age 16, Sam would have been about 8 years old when she was born. Even if Mark was not born until 1870, Sam would still have only been about 12. Anderson was made up to look older, but the casting was still far from optimal.