I fall inline with Rand's view, at least in the context of western wildernesses. Few are as pedestrian as those we were on in the Hermosa Creek area (I don't think motorcycles and bicycles are permitted in designated wilderness areas), especially as one gets to higher elevations. The trails are more 'bedrocky'. I'm reminded of some letters to editor in the local Flagstaff AZ paper, where mountain bikers complained about the local hiking club's trail maintenance because they took out the obstacles (small fist-sized to loaf-of-bread-sized rocks, small boulders)...they craved the challenge.
I suspect I am entering the realm of personal choice, but I think that both the mountainbikers that seek the challenge of obstacles and high speed transit, and marathon distance runners of similar character, aren't "getting it", wilderness-wise. At the end of their trip, they just have this blurry, bouncy mind video of whatever was within the 20' tunnel of vision.
My trail maintenance days on the Kenai Fjords NP Exit Glacier Trail, were primarily due to marathon runners cutting straight down (and up, for that matter) through the switchbacks put in to keep the percent slope of the trail moderate (not so much for ease of walking, as for minimizing erosive overland flow of rainfall). It took many volunteers several seasons of carrying jute netting and many hours to stabilize the slopes denuded of vegetation by the extreme sports runners. While this isn't a common problem with mountain bikers, I agree with Rand that even light traffic in some soil types leads to dusty trails, and where moist soils are prevalent, wheeled conveyances are more erosive than the other transport means. Perhaps most significantly, wheels are prone to leave ruts, which can become channels for water to be further erosion of trail.
But I guess my biggest rant on mountain bikers has to do with attitude...so many are so into their rapid descent, that they presume they have the right of way, whether the "impediment" be horseback riders, backpackers, family's hiking.
Okay, I know, enough already...; ~ }
I've done a fair bit of mountain biking, and it is striking the amount of damage a bike can do to a steep and winding hiking trail versus a well graded dirt fire road like you find in Hermosa creek.
I'm a little puzzled by the burning desire to ride bikes in wilderness area. Don't most of these areas have plenty of adjacent Nation Forest Areas to ride in, if that is what you really want to do? I mean it -is- nice to ride in a beautiful area, but anyone insisting they take in as much scenery as one would hiking is a complete idiot. No, if you're on a bike you're there primarily to ride...at which point someone will come back with ease of access arguments. I find this argument pretty lame too, if an area is set aside as 'Wilderness', does this not imply that ease of human use is -last- on the priority list, and preservation is first? We've got plenty of National Park's in beautiful places where 'ease of access' rules the priority list.