I've run weekly over the San Juan Trail off of Ortega Highway in southern Orange County.
Mountain bikes have ravaged these trails far beyond nature's wildest efforts. Don Douglass speaks of tires passing over the terrain with less impact than a hiking boot or a horse's hoof. What he doesn't mention is that tires do not roll over turns and switch-backs, they dig into and groove the trails. Not only is the trail left with permanent scars, but add a rainstorm or two and the groove becomes a 6- to 8-inch trench and the rest of the trail begins to wash down the mountain.
In a few years of trail bike use, this process has destroyed large sections of the San Juan Trail. Unregulated use of the area can only have devastating consequences to similar trails.
Common sense reveals Douglass' remarks as protective of selfish interest and avoiding the harder questions of how recreational resources can be reserved and at the same time shared by multiple users.