Bill, we were out at Sycamore canyon Riverside on Sunday and did Peters canyon on Saturday. Most all of the places around are ride able on the tandem. Most of the trails we even pull Adam on his bike.
I just rode Santiago Oaks on my single last week and the new trails look like they would be a blast on the big bikes. Some other places we've ridden are Aliso, El Moro, Turnbull, Whiting (Whiting to the Luge was a kick), Bonelli, Cheesbro, Sycamore Canyon (Pt. Mugu).
We just set up our sitter to watch Adam one Saturday every month so we can get out on the bike and not have to pull him up some of the hills, unfortunatly our Feburary date is this weekend (the 19th) and it looks like rain......maybe next month.
The only thing to worry about is crowds. The big bikes attract them, a group of big bikes more so.
BTW what trails do you ride out at Chino, maybe you coould show us around sometime?
Anyway keep us in mind, we'd love to meet up again.