Ok, that was what I thought. I have a very large rotary hammer drill so going into asphlat won't be a problem. But again, I can't directly bond that rod to the AC ground rod, I can only run the 35 ft cable back to the SPG, which in turn is connected to the AC ground system.
That is fine. The point is to connect the two ground rods together, which you will do by connecting to the SPG. You don't have to connect the shack ground rod directly to the AC ground rod. You just have to make sure they're connected together--even through a single point ground.
I did look at your diagram. No, you do not 'need' the station ground rod. If there was an easy way to do it, I would suggest putting that ground rod at the other side of the house, where the co-ax enters the building, about 16 feet away from the first ground rod there. However, I do remember you saying that that area was asphalt covered, and it would be hard--if not impossible--to run a cable between those two ground rods.
All in all, being in a area where lightning isn't really a problem, you can get by fine with the ground at the co-ax entry point, the SPG for your shack, and the AC mains ground rod.