I might suggest, if your interested:
http://www.ur.com/index.php/locator/search/?address=&city=Phoenix&state=AZ&zip=85002&country=USA&searchAreasAll=Y
They rent things like tillers and augers.. I got a hold of a tiller and worked for a weekend in our yard. Till down the 4-6 inches then use a shovel to move it all over.. Till another 4-6 inches and repeat. Do this until your satisfied...
Now get some nice top soil and till that back in with the soil you removed.
Anyways, the link is for a company called united rental and it is a few of the locations up near Phoenix. We use Erv's Equipment when we need to rent stuff like this, but Erv's is a local Tucson company.
The whole back yard is like that, you dig down about three to four inches and then hit this rock hard aggregate zone. Whacking it with a hand pick slowly breaks it up but OMG it's hard work. Good thing the wife doesn't want to plant Spring bulbs....