A novel by Frank Herbert.
Santaroga is a town in California that is considered odd because it does not act like an American town is supposed to. That is, it doesn't buy the most popular things, people don't move, salesmen leave, chain stores go out of business,... you get the idea.
Turns out they have a supply of a unique fungus in the local caves that is chemically similar to LSD which prompts a different state (implication of a higher state?) of mental consciousness. The hero is pulled into the chemical trap...