At the end of the tutorial you have the choice to settle down at one of the 3 nearby towns (Foothills, Plateau, Valley). Each choice is associated with a achievement, it will unlock
AFTER arriving and claiming the settlement.
For the Achievement " Ten Thousand Gallon Hat' you will have to choose the Plateau.
The video included shows the choosing process at 20:45 and the glaim of the settlement at (unlocking the Achievement) 36:05.