Motocross outfitters Thor have just started making crossover mountain bike riding gear, and these Static zipoff shorts/pants are a great start.
The shiny, crashproof ballistic nylon shell is reinforced with ultra hardwearing Cordura across the seat, a stretch strip across the crotch adds a bit of mobility among all the heavyweight fabric and the slanted cut helps movement. They do get hot after a while but a wicking mesh back panel and full mesh liner reduce trickling sweat to a minimum.
Rubber logos on the cargo pockets add a little more protection and the light foam hip pads are velcro'd into the waistband. The low price for zipoff pants protects your wallet too.