Answers:
those are not california wine categories, they refer to the wine, the grapes and the process of making them. This detail of grapes explains where most of the name come from.
Other Answers:
Califonia names their wines by the grape a bit than by the region like several old world countries do. Each grape have different characteristic. Pinot Noirs are the lightest within color and also usually in tannins. Merlots are within the middle range for red wines. Zinfandels tend to be the heaviest red wines near robust flavors.