Here is an all girls mountain bike group my cousin rides with out in the Black Hills of S. Dakota. Looks like they have some nice XC trails, just look out for the buffalo.

http://www.rapidcityjournal.com/pages/slideshows/88/index.html

Irene is the 8th picture in the slide show.
Sounds like they get good participation.
 
Alone in the woods, who stands to be King?

That's cool. Too Bad we can't seem to get that kind of women's participation here.

Ryan