I find the Ciclosport 434M works pretty well for grade measurement, and since it records, you can check on climbs later.
For Balcolm Canyon the steepest grade for a 20 second increment I see on the recording I have is 25%. But then it was in the middle of a brutal double century, and I was going like ~4.5 mph on that section, so it might not be that accurate. For 1/3 mile its 15.5%.
Adding ~10% to that steepest pitch on Balcolm makes Fargo seem pretty brutal! I have to try it someday, but falling on that hill doesn't sound too fun.