One of my homes borders Mt. Diablo State Park on the north side. We always called this route the 5 Summits because you summit 5 named peaks:
Twin Peaks, Eagle Peak, Diablo, North Peak, Olympia
This is an awesome hike that we use as training for the Sierra.
cheers and good page
I know author already mentioned this but just wanted to reiterate. There are a ton of trails on Diablo; many of which are not listed on free map. Worth the $6 for sure.