Here is the full list of all 18 Sierra Madre: The Wild West achievements.
Start a new game.
Complete the Delivery mission by driving a wagon from one town to another.
Hunt down an outlaw by completing the Hunted mission.
Liberate a town from being harassed by outlaws by completing the Town Liberation mission.
Liberate the town of Mina.
Liberate the town of Desolation.
Liberate the town of Canyonville.
Liberate the town of Foresterville.
Liberate the town of Bandito.
Liberate the town of Jim's Town.
Liberate the town of Lakeside.
Kill twenty bears and sell their hides.
Kill thirty boars and sell their hides.
Liberate the town of Plateau Flats
Accumulate a thousand dollars.
Accumulate ten thousand dollars.
Accumulate a million dollars.