Here is the full list of all 24 West of Dead achievements.
Defeated first Outlaw
Helped the first lost soul
Defeated the Preacher (I)
Completed the Mines
Completed the Hunt
Found the first rune
Completed the Crypt
Completed the Bayou
Completed the Canyon
Completed the Farm
Completed the Town
Completed the Graveyard
Completed the Church
Defeated the Preacher (II)
Defeated Injustice (Preacher III)
Banished Injustice
Found the second rune
Found the third rune
Helped 10 lost souls
Helped 50 lost souls
Defeated 10 Outlaws
Defeated 50 Outlaws
Found the fourth rune
Completed the Battlefield