I talked to a Chinese person at work. He indicated the mystery characters were a mix of Chinese and Japanese - which just means it's Japanese, since the Japanese have a complicated writing system that includes a lot of Chinese characters. My friend could make out a word for mountain and a word for moving from left to right.
So at lunch I went to the main library and started trying to figure it out from Japanese-English dictionaries. I had made only primitive progress after twenty minutes.
Then I saw an Asian gentleman browsing the Japanese book section. I asked him if he could read the characters. He certainly could.
Well, it has words for Mountain Rock, and some part of your leg, but he wasn't sure what they were trying to say in the last few characters. He could pronounce the last few characters - which were Japanese sound-it-out writing, I guess - but he wasn't sure what they were trying to say.
Based on all this, I speculate that the characters say some equivalent or some part of Rock'n'Sole Trail Challenge - which was the name of the race.
I ran in a hot, hilly race
Then went on a wild goose chase
Attempting to glean
What the characters mean
That fill up my shirt's frontal space.