Santa Maddalena is a religious community situated in the north-western region of the Sonaran Desert, an area largely populated by red strain infected. Led by Jack Vermillion, the group is shown to be weak in tactics and combat, as seen if they're attacked by Los Ceros in the Sonaran War, Santa Maddalena is annihilated if the Survivalists choose to not aid them in the battle.
Santa Maddalena was founded by Jack Vermillion somewhere between the beginning of the apocalypse and Joe's departure from his bunker (a year later). He found the church of Santa Maddalena while fleeing from a group of infected. Presumably, after taking refuge in the old church he received a message from God. God told him that he caused this apocalypse to punish mankind for their sins and compared this catastrophe with that which happened in the time of Noah. Jack was named by God as a new Noah and told him to join a flock to teach them his wisdom and lead them out of the desert when the time is right.