Humbug's Gulch is a Western-style theme park that is a part of the "Humbug's Gulch" franchise, and one of several parks of the same name in the state of Texas. John Dorie would work at one of the theme parks at the weekend.
It would appear that after the outbreak that the park was largely abandoned, apart from a scattering of survivors. John Dorie and June came to one of the parks in search of guns and ammunition, as John knew from his time as an employee that the park kept these items for when the trick shots would entertain the crowds. They got got trapped in the park and came across Dwight, who was searching for his wife.