>>371120In Marin County, California, the alleged birthplace of the mountain bike industry, there are almost no legal singletrack trails. Oldfags like me remember the time before the "no bicycles" signs went up. Gary Fisher once told me that, years before anybody gave a fuck, he was riding his bike on a Marin Municipal Water District trail, and encountered a ranger. The ranger was impressed by his cool bike, looked it over, said "wow," and all that, then told him "well, um, you know, technically it is illegal to ride your bike on MMWD trails, but have a nice day." The problem is that little old ladies on horseback, who control everything in Marin, decided that mountain bikes are dangerous to them, as they are perched upon a half-ton animal with a walnut-sized brain, so the "no bikes" signs went up all over MMWD trails. MMWD even commissioned a study to see how much damage mountain bikes did to trails, compared to horses and hikers, with the goal of using this study to ban bikes entirely, from the dirt roads as well, but the study indicated that the bicycle riders did the least damage, so the MMWD buried the study, and you can still ride on the fire roads legally. It's an entirely political issue, and in 30 years the mountain bikers haven't made much inroads in that department. I think they relish their status as "outlaws" and "victims."
I used to ride my bicycle, legally, in Point Reyes National Seashore, first time around 1972. Point Reyes used to be dairy ranches, criss-crossed with roads, some even paved. Parts of the peninsula were designated as "Wilderness," and they attempted to erase the history of ranching, logging, and mining. I rode the "trails" (old ranch roads) there legally until 1984, when the Wilderness Act was interpreted to include a bicycle ban. tl;dr Bicycles cannot be ridden on USA Wilderness trails because they are mechanical, unlike oar-locks and skis, which are "natural" or whatever.
Pic is why you can't ride bicycles on trails in Marin.