The Polly Ann Trail is a 36.7-mile long, non-motorized trail in Oakland and Lapeer Counties, Michigan on a former Pontiac, Oxford & Northern Railroad corridor. 

The portion of the trail in Oakland County has a crushed stone surface and runs for 16.9 miles from Orion Township to the Oakland–Lapeer county line. Certain sections of the trail in urban areas have an improved asphalt surface. Along the way, trail users pass through the communities of Orion Township, Oxford Township, the Village of Oxford, Addison Township and the Village of Leonard.

An open space park/mountain on the edge of Golden, CO.   A very popular and well defined  loop trail for mountain bikers and runners.   I think it should be on the list!  

There is a Strava segment for the CCW loop starting at the Mesa Spur Trail.  There may be other segments for this loop, starting other places or running CW.  You must beat the Strava times to claim the FKT!