Corrected entry: The couples are supposed to be taking their vacation in January, yet when they arrive at the RV park, there are people swimming in the pool.
Corrected entry: Director Jack Starrett claimed he hired real-life Satanists as cult-member extras.
Correction: Word for word copy from IMDb.
Correction: However, they are in Texas and it's warm enough to swim in January (especially since most pools are heated). Most of the time they're in central Texas, but even accounting for being near Amarillo, if you look at historical temperature figures, in Jan 1975 in Amarillo, there where days were it was more than 70°.
Bishop73