Hmmm, Google Maps does not seem to recognize Dayton as a locale in Mason County, but my Delorme PC maps do show Dayton as a placename in Mason County, (as well as the more well known Dayton in Eastern Washington). Here's a link to that region on Google Maps:
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maps.google.com]
The Simpson railroad tracks are the curving line running through the mill yard and then north of but generally parallel to the West Shelton Matlock Road shown on the map. If you zoom in enough, there is a Dayton Store and a Dayton Westside Fire District station along the road.