Pulled one from the ground and the bottom, around the stem, was brownish, grainy, and had worms. The center was the pretty white of a good mushroom. I've not seen one rot from the bottom before.

Any ideas...was the top still good? I did trash the whole thing but more are coming up.

I imagine it was the worms that got it rotting, it's always a race who gets the good ones. You could have just trimmed off the rot but if there is lots just grab the ones that have not been touched by worms. Mushrooms can appear at different times each year or not at all. I have never heard about picking to soon, some times there is no flavour to them though.