The hippies here are depicted as, to paraphrase Vegetales, "the hippies who don't do anything." They have great ideas on how to improve the planet, but have no motivation at all to set things in motion.
The boys wear Che Guevara shirts, which Matt and Trey lampooned in SP:BLU.
Linda Stotch is city treasurer and has either an engineering degree or experience as an engineer.
"My son is in there!" - from Siege 3.
"Were you bit" and "Listen, you're my friends, but if you've been comprimised, I'll have no problem taking you out! I'll expect the same from you" - from Dawn of the Dead.
Armageddon was written all over this one. Check it: The set (the glass wall with the red lines all over it). Chef was Michael Clarke Duncan. Butters' mom was Ben Affleck (the one with a loved one at home). Cartman was Bruce Willis. Randy was The four of them walking down the walk way with the crowds cheering. The shape of their little machine..
When all the adults are talking about fixing potholes, Cartman barges in and starts talking about the hippies just like the dude is talking about the storm in The Day After Tomorow. For example, Cartman says: "2 hippies are coming here every second' and that one dude says: "The tempeture drops (some number) every second.".
The whole episode follows the exact story line of The Core.
The hippies were a jab at Ward Churchill, head of the department of Native American Studies, who wrote a paper saying that the US was asking, nay begging for 9-11 to happen and that the people who died in the Trade Towers were "little Eichmanns." The hippies used "little Eichmanns" several times in the episode.
The WoodStock flashback with Stan's parents refutes Randy's flashback in "Something You Can Do With Your Finger." Woodstock took place in 1969, and if Randy and Sharon were 19 at that time, they'd be 54-55 now. Mr. Garrison would be in his 70s.