Here's a picture of the garden after the second year I started it on a previously quack grass sod clay laden soil. The harvest was bountiful for squash, corn, melons, cukes, brassicas, leafy greens, etc. This is in zone 3, which has about a 100 day vegetable frost free growing season.
Basically, I set out in steps to get the soil amended and encouraged to grow so well.
First, I covered it over in the previous early fall with a thick canvas and plastic layer to kill the growth underneath. In spring, where I didn't have areas covered, and to extend the size of the garden I spread out clear plastic to solarize the growth underneath.
After a few weeks, the plastic was removed and the area tilled.
Then, buckwheat was broadcast for a green manure.
After about 8 to 12 inches of the buckwheat growth, I tilled that into the soil.
Then raised beds were raked up where everything but squash was growing.
The squash areas were made by dumping several buckets of rotted manure/compost into the holes dug where the squash was to be planted. The areas around that were tilled until the squash spread out and kept the shade to keep weeds from growing.
The corn was tilled between the rows and the areas where corn was planted was raised up by the hiller, furrower attachment on the tiller as it was being tilled. This also was used to cultivate until the corn was tall enough to easier weed by hand.
Basically the 'usable' soil of clay/loam which was aided by both tilling after the plastic and green manure plowdown (buckwheat in this case), which was the soil raised in beds that was amended by the green manure. We even grew carrots by the second year as the soil was worked to loosen it more with fall rye planting that was tilled in spring and more buckwheat or oats as till in green manure. Chicken and duck manure from the pens also supplemented the soil along with any and all compost that could be made.
Clay can be problematic when it's a prolonged wet season and is hard on roots packed tighter to get nutrueints once that dries out too. When there are prolonged dry spells, it pays to water the right amount....which on average should be the equivalent of 1" rainfall per week.
Mulch
Green Manure plowdown (or 'till in')
Compost
Raised beds
all the above do most to benefit poor soils, including tough clay.
The Rocks ...we have plenty of them. They are removed from the garden into a convenient pile area which attracts garter snakes, toads and such to help pest insect control.

But, don't get the rock piles too big that they might attract woodchucks or skunks.