Carlton has spent more than three decades documenting the history and culture of his native Wahkiakum County and the surrounding areas of Washington and Oregon. He is regarded by historians and museum professionals across the country and in Finland as a significant historian and scholar of southwestern Washington and of the Finnish immigrants who settled in the northwestern United States. He has written books about the following southwestern Washington areas: Knappton (1964 and 1975), Frankfort (1965), Brookfield (1966), Pillar Rock (1969), Altoona (1972), Deep River (1978), and Cottardi Station (1980). In A Pioneer Scrapbook of the Columbia River North-Shore Communities: Wahkiakum and Pacific Counties, Washington (1986), he presents a selection of historical features about the area–news stories, poems, special reports, narratives, and photographs–many of which had also appeared in the historical supplements that he published in local telephone directories for the previous 20 years.