I'm not sure Garmin offers a MTB trail map. You can certainly find some tracks to download on the internet. I've stole some off of motion based before. Maybe someone else will chime in, but I think most MTB trails are not well published, and might change more often than roads or topography. I have some old topo stuff from garmin and some times trails are marked, but most of the time not unless it was an old railroad or maybe a dirt access road.