223M is the lower section of this same trail. On the national geographic map they're both named "Nimblewill C-spur." No one calls them that. Both of these sections of trail fall under the name "Turner Creek."
The Turner Creek trail is, simply put, one of the best pieces of singletrack in the Bull Mountain trail system. Obviously, it's the most fun going down, but makes for a good singletrack climb as well.
When descending from the very upper end of the trail, be sure to bear left at the triangle junction, and drop down onto the grassy doubletrack. A little ways down the doubletrack, be sure to hang a hard switchback left turn back onto the singletrack.
This lower section of singletrack is fantastic, thanks in large part to the fact that horses aren't allowed on it. Consequently, it stays very narrow, tight, twisty, and is a rocking good time!