"Are you looking for an exact distance, or for a challenge category?
Trails are trails, with twist, cant, and camber. They go from here to
there, some following contours and going around obstacles in a rolling ,
sinuous, graceful style, others marching you straight up hills or
through ankle-biting rock gardens.
The traditional distance categories belie precision--50Ks around the
country include races from 30.2 miles to 34++ miles; 50-milers have been
known to be 48-53 miles, and 100Ks or 100-milers can range in mileage
from a little under to when-will-this-thing-end.
We have the illusion of accuracy from GPS and Garmin devices, but
really, isn't not knowing part of the fun?"
--Tia Bodington, Ultrarunning, Sept. 2012 issue