"To get all the California County summits you have to climb stinkers like Mount Diablo."
But then you could try heading over to the north summit. As far as I recall there are antennae but as my girlfriend learned the hard way - nobody goes there. She sprained her ankle while downclimbing from the main summit and was rooted there for a whole day. We didn't miss her until 5 p.m. when we started rousing the rangers. About two hours later she was picked up by some maintenance guys who had done whatever there is to do with the installations on top.
Mount Diablo actually has several excellent climbs, both strenuous and rewarding, with surprising solitude (for being so close to millions of people). I have done hikes on the mountain on any given weekend and rarely do i see many other people. Of course, like a lot of other peaks, most people are only interested in the summit and do not venture 'off the beaten path'. These poor souls miss the true beauty of the mountains, and are bound by this "summit mantra".
You screwed up.....and then you kept screwing up.....and then you blamed the mountain. These are rookie mistakes.
If you want to discover Mount Diablo you have to start at the bottom and take it all in on the way up, around, over, and through all of the beautiful things that are 'The Mountain'. You drove passed all that makes up the mountain to stand at the summit--that's some boring shit. Here's what I do:
Eat a big breakfast, drink some coffee, make a big poo, and put on some proper running attire. Start from any angle (I'm on the Shell Ridge side) and start running. Of course you'll want to have a plan until you learn the mountain, so bring a map. The trails are filled with diversity. When I come up over Moses Rock Ridge and look out at the north side it's like a whole different land. It gets me every time. Coming up Wall Point you get great views of San Ramon valley and of the mountain. The Wall Point trail itself is an absolute work of art. From there you can go up and do the Walk Through Time that ends up at Juniper (fabulous!) or take a right turn at Devil's elbow and get some views of Morgan Territory that just aren't available from the roads.
For a short crazy steep trip up the mountain, start at Macedo Ranch, run up Wallpoint to the Summit trail, then go right up to the top. It's hella steep, but it's only 6 miles each way. When you get to the top and there are all those cars and people you won't care, because you will feel too alive and you will be part of the mountain, unlike them (and you on your last trip). When you get back to your car you will have quite a different perspective of the mountain, and you will have a deeper respect for what your own body is capable of. Try this just once and you'll be back for more.