Around the 52 minute mark a modern Ethernet switch is clearly visible in the Sheriffs office on top of the filing cabinet.
Set in the seventies, the police radios shouldn't have digital squawk sounds prior to voice when sending and receiving.
The film is set in 1979 but makes references to "An American Werewolf In London" (1981) and "The Shining" (1980); see Movie Connections.
Set in the seventies, yet the phone book lists numbers in the 360 area code. The 360 area code (which covers western Washington state) didn't come into service until January 15th, 1995.