Maryhill Stonehenge.

From the website:

This is a full-scale replica of England's Stonehenge built in the 1920's as a memorial to 13 Klickitat County men who died in World War I. According the the plaque onsite, it was the first monument in the nation to be built and dedicated to those who gave their lives during the first World War. There is a neat diagram near the monument that shows how it (and the original Stonehenge) can be used for astronomy. Sam Hill, the Quaker pacifist who was inspired to built the monument after a trip to England, is buried a few hundred feet behind the monument overlooking the Columbia River.

Link

Update 4/8/06: Sherry Reedman suggested another replica of Stonehenge: http://www.alfredshepperd.com/Stonehenge/main.html (Thanks Sherry!)