Originally Posted by axolotl

I grew up near the towpath and biked on it often when I was a teenager, including sometimes on narrow tires. When it's hot outside, i.e. in the summer, the towpath dries very quickly. (The same was true on an unpaved trail I used to commute on.) That's one reason why I recommend that people only plan to bike the entire length of the C&O Canal in the summer. When there's a downpour from a thunderstorm in the summer, it will get muddy, but usually only remain muddy for a day or two. After rain in the spring, winter, or fall, the towpath will remain muddy for much longer.

Personally, I found all of the embedded rocks to be a bigger annoyance than any ruts.