I'm in Australia and would love to check out that area one day. Where in the US exactly are these and are they spread apart or in the same general area?
If you're wondering about visiting locations, two pieces of advice:
Go to the Twin Peaks Festival and take the guided tour. Absolute best way to get this done.
http://www.intwinpeaks.com/2008/02/locations.html?m=1
If you really want to do it solo, this site is invaluable. Click a picture and you can learn about the location, often with a Google map coordinate. Both the Washington locations and the California locations are catalogued.
(If on mobile, view the web version. Mobile version sucks)