Duncan wrote:

I suspect I'll be taking my hardtail so not so keen on the double diamond /
free ride north shore aspect but still like it pretty technical.
Comfortably Numb in Whistler was one of my favourite trails.

I suggest that you look at the book "Mountain Bike! Northern California"
by Linda Austin. Look at the section for "East Bay Area" starting on
page 334. Lot's of good rides in the East Bay parks. I'd stick closer to
Berkeley, as it gets very hot further out in the east bay. Also look
at the "Gold Rush Country" section starting on page 141, and the "Around
Lake Tahoe" section starting on page 199. The ride descriptions are very
detailed, with both aerobic and technical difficulty listed. Again, I
highly recommend the east bay rides around the Berkeley area.