This episode is sometimes titled "Flashbacks" in the TV Guide listings.
In the first flashback, Cartman Gets an Anal Probe (1997), the actual episode clip is shown, then characters are shown in their current, computer animated forms, as opposed to their original, construction paper forms, which is what the first episode was made from.
This episode shares its name with The City on the Edge of Forever (1967). One of the students on the bus is wearing a red Star Trek (1966) uniform. In the series tradition, the characters that wear the red uniforms are often killed off if not the first to die.
A guide tells people on tour of the mountain area that "red-bellied" Chickadees are indigenous of the area. Chickadees in reality are referred to as Tits. There are four Tit birds native to the state of Colorado, however none of them are red-billed.