Trust me, I am not encouraging anyone to try riding up the mountain and then riding back down all day; besides skirting Diablo as a business, riding up the fire roads is downright dangerous when you have guys reaching 40+ mph coming the other direction. I based my response off the events of Diabloween a couple years back, and I imagine if you rode up the fire road on the back side of the mountain (eventually coming up by the start of Tempest), made one run down and then rode back out to Rt. 94, no one would give you any problems.
Keep in mind, Diablo is developing and expanding the XC loop that has been left to ruins up at the top of the hill. They were talking about cleaning it up and carving out some more challenging and better flowing lines - I imagine when it's done, they will offer a discount pass to ride the lift up once and spend as long as you'd like in the XC area.
But regardless, Diablo was not built to cater to cross country riders and will never put any emphasis on it, so you guys better shed the lycra, strap on a full face helmet and give it a shot!
