Soil Issues

What passes for bagged topsoil/garden soil in these parts?

In Michigan we'd call it 'mulch' - all chopped-up bits of wood, with some dust thrown in the bag to increase the weight. 

Do the people in Phoenix really grow flowers and vegetables in this stuff?  All I can imagine is that wood breaking down and starving the plant of nitrogen. 

I guess I need to find a good source of compost.  And if that looks like shredded wood, I'ma gonna run screaming. 

Handicaps I expected, but dirt I was thinking I would be able to buy.