How about Old Priest Grade? Two miles averaging 13.4% with a nice last step of 17.7%. Since it's on the way to Yosemite, I have always climbed it with a touring load, so perhaps it always seems longer and steeper than it would on a naked bike.

On one trip many years ago, I rode up ahead of my wife, thinking I would enjoy a nice cold soda at the cafe at the top while I waited. I was disappointed to find the cafe had burned to the ground, but when not a single car came along in the quarter-hour I was waiting for my wife, I began to wonder what was going on. When she arrived she told me that a pick-up was having trouble going as slowly as she rode, and there are very few places to pass. Then the pick-up lost a boat that had been poorly strapped on. The folks in the vehicles behind helped load it back on. After this fiasco, the pick-up driver had a lot of difficulty getting his vehicle going again and appeared to burn out his clutch. He never did arrive at the top and we always assumed that everybody backed down the hill so he could park at the bottom and get a tow.