Treharne is a place name associated with a location south of Vernonia near the intersection of Timber Road with Highway 47. It is unknown to the sixth edition of Oregon Geographic Names. It does appear on a number of older maps however. As a community Treharne has always been dogged by the lack of suitable water. The Valley is broad and flat and very attractive, but wells in the area generally produce little or no water or salt water which is a problem.
Treharne features a grocery store/deli, formerly the Sunnyside, but now called the Treharne Grocery. It also has a phone booth, and one of the Vernonia area's famous bridges with a square corner in the road at the end of it, though a construction project was started in 1995 to change this. Extensive flooding occurred in the area in the great flood of 1996.