OK, let's escalate: Which is harder -- the Pikes Peak Marathon or the MMWT? Let's assume running for both courses.
That is one big assumption for a lot of us.
Having been on both mountains several times, it's gotta be Whitney - right? There's a nice, graded, reasonably-sloped road to the summit of Pikes, which I assume is the track the marathon is run on? I'm going with a key on the word "harder", not longer - smooth grade versus rocky, gnarly trail.
The only easy way on Whitney is to take the tram and grab your Starbucks at the top . . .
