Hmm, here are some ideas (I just really like coming up with classes)
- Medicine Man
The primary function of these "medicine elders" is to secure the help of the spirit world, including the Great Spirit (Wakan Tanka in the language of the Lakota people), for the benefit of the entire community. Sometimes the help sought may be for the sake of healing disease, sometimes it may be for the sake of healing the psyche, sometimes the goal is to promote harmony between human groups or between humans & nature. (Wikipedia)
Your healer / druid with a more metaphysical approach. Seeing how we're talking about western styled classes, magic would not be common and would probably be heresy - sensing interesting quests ideas

. Seeing how the rituals were timely and used herbs and other substances, gameplay wise he or she could be limited by charges in combat - a couple of uses max each fight, so deciding when to use the stun and heal could be crucial, representing the need to restock between fights. Alternatively you could go the pokemon skill charging route, where skills are exceptionally powerful, but take multiple turns (2-3 maybe? anything more would be boring) to perform the ritual.
- Gold Miner
Some background info on the Gold Rushes:
A rush typically begins with the discovery of placer gold made by an individual. At first the gold may be washed from the sand and gravel by individual miners with little training, using a gold pan or similar simple instrument. Gold rushes were typically marked by a general buoyant feeling of a "free for all" in income mobility, in which any single individual might become abundantly wealthy almost instantly, as expressed in the California Dream.(Wikipedia again)
Given the historical background, those people were usually self-sufficient, capable of surviving on their own and defend themselves even though they were constantly under a threat. When compared with traditional classes, I'd expect one to be a mixture of a hunter and barbarian. A capable melee fighter with a pickaxe and a shovel and a skilled hunter that uses a bow - living in the middle of nowhere forces one to hunt for food. Needing to be able to survive alone, I'd expect the class to come with a lot of self buffing and healing skills, like first aid and overcome pain. Overall a lot of survivability and damage, but unfriendly towards other party members, lacking support skills.
- Highwayman
A highwayman was a thief and brigand who preyed on travellers. This type of outlaw usually travelled and robbed by horse, as compared to a footpad who travelled and robbed on foot. There is a long history of treating highway robbers as heroes, originally they were admired by many as bold men who confronted their victims face-to-face and were ready to fight for what they wanted. In the 19th-century, American West highwaymen were known as road rangers. (You guessed it, Wikipedia again.
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Potentially a rouge counterpart, but your crucial feature here could be the horse which leads to interesting game mechanics. Buying new mounts and picking the best one would be fun in itself (maybe even getting exclusive ones from making friends with native american tribes? Fun stuff.) and it would also mean being probably the fastest character in the party. Skills could hit a lot harder when you ''charge'', corresponding to being affected mainly by your agility. Also you could potentially charge into battle, with having two states applied at the begging of every fight - one that is a massive Agility boost to represent the charge, other one that decreases agility every turn to represent the horse getting tired.
Should be good enough for now, I'll post some more if I have more ideas.
