Fire roads around here are not very challenging, mostly remnants of ranch roads and thus suitable for driving even with a trailer. They teach the basics of pedaling on gravel and rocks but are fairly pedestrian compared to the twisting and turning up and down of the single track. I personally avoid them because they are where you usually find the dogs, leisurely hikers and kiddos, I feel it is safer to use them as connections to more single track. But in NM they are steep and go straight uphill and would be excellent training ground.

I am not aggressive but I enjoy mountain biking on my overkill 5" travel trail bike. We have tons of rocky trails around here so maybe one day I will get more skilled, I consider myself a forever newbie. I generally like downhills but we don't have any true "downhill" courses. Creek crossings I hate because I am scared of water snakes!

And because I think it takes all types, anyone who rides off road is mountain biking to me. Some of our locals think if you ride X trail you aren't really a mountain biker but you have to start somewhere. If you are considering riding crushed granite mountain biking, I will encourage you to try a fire road, if you are only riding fire roads I will recommend my favorite beginner/intermediate course. I remember being freaked out at the feeling of a gravel fire road, so I try to encourage any newbie who is trying out my favorite type of bike riding.