You could ride out along Camino Tassajara after climbing Diablo - there's some nice countryside out that way, and then loop back around San Ramon to Athenian (if that were the start point). That's probably get you 60+ miles given that Diablo is 11miles one way - this would be somewhat similar to Ron's Post Thanksgiving route last year IIRC. Having said that it would be a pretty flat ride afterwards, and there may be some more exciting/epic options if you were so inclined.