Just a thought but you might want to take I90 one way and I94 the other then you could get caches in north Dakota as well as South Dakota, I recommend GCGG6C and GCM8XT in ND,
I grew up in Reno Nevada, My dad and uncle were real cowboys leaving home as teens and working ranches all over the west...So its in my blood, the name is for my home state and to honor my dad and uncle.