I was looking at the maps on mytopo.com and noticed a trail along the Clackamas River, starting near Indian Henry campground and proceeding south along the west side of the Clackamas and then the Collawash River, ending at a quarry across the river from Raab campground. Looks like a distance of 7 or 8 miles. Here's the map. To add to the peculiarness of it, the trail is identified as number 564, which is the number for the Rho Ridge trail. I have not seen this trail on any other map, recent or historical, and I'm wondering if it has any basis in fact, or if it's just a figment of some bored cartographer's imagination.
mytopo.com claims that they use the latest topo maps, and as far as I can tell, this particular map is dated 1997.