From my view Fort Yamhill represents an example of one of the many forts and Posts that would have been managed and supplied from the Vancouver Barracks as part of the Columbia Department. This puts it in as part of the Portland Story. It also is part of story of what happened to the first inhabitants on this land and in Portland.
Fort Yamhill was established in 1856 as part of the relocation by the army of the last of the native population to reservations (call the trail of tears). It was positioned to keep natives in and keep settlers out. But when you look at the placement of the fort is was mostly just to keep the indigenous people on the reservation. By 1866 with natives pacified and with demand of the from the civil war in the east the fort was closed.
The Oregon State Parks opened the Fort Yamhill State Heritage Area in 2006. What is known about the fort today comes from archaeological excavations and limited historical documents. From this the park service (and I am sure on a limited budget) has attempted to give visitors an idea of what Fort Yamhill was and its roll in Oregon history. Today you can do a walking tour of where the fort was and read signs that tell a little bit about Fort Yamhill.