Take a look over at the square-foot gardening forum on this webpage and it's related FAQ guides. Sounds like your 10' x 10' area is a perfect match for it's basic principles.

In my case, I only had a very small 15'x15' area that receives six hours of full sun with everything else on my property being less than four hours of full sun, so the SFG was a good choice for me to optimize my growing space.

I also live in an area where the soil is so hard, so "red clay" that you need a pickaxe to get more than 2" deep into it and, even then, you'll likely only get about 6-18" deep before you hit lithic bedrock. Fun stuff, huh?

Below are a couple images of how I'm utilizing that space under the square-foot gardening concept (lots of plants in a very little space) ...

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As for the soil, if you follow the link below you'll find his recipe for "Mel's Mix" which is 33% vermiculite / 33% peat moss / 33% homemade compost - or really anything other than pure city compost. I was fortunate enough to have an abundance of compost as I use composting as a way to organically reduce my landfill waste. ;-p

Only 364 days until the next Earth Day! lol...

Here is a link that might be useful: The Official Square Foot Gardening Homepage

If I have the right county for you, try these links for your county's gardening resources.
http://ccmg.ucdavis.edu/
http://cecontracosta.ucdavis.edu/
Now, you have a couple options. Most people do a soil test, altho I never have. Contact the above resources for info on this inexpensive test. Ask specifically about lead and other toxins, do they even test for that. Some folks dig or double dig and add in organic matter. If you have compost, use that, or you can usually buy it in bags or bulk from nurseries or the city or county. Again, the above links should know this. If I have to buy "soil" for a garden I buy "humus" or "composted manure" never "topsoil" becoz it is heavy and void of much nutrients. I would not use container soil or potting soil, either, as that is a very light mix made esp. for container plants. I like another method called lasagna gardening where you just layer cardboard and/or newspaper, wet it, then add your organic matter or compost/humus (as described above) several inches high into a raised bed and plant. This is also called no-till gardening. Underneath, the cardboard and newspaper will be decomposing and killing off the grass or weeds underneath becoz there is no light getting to it. Just like if you lay a bag of soil on the grass and in a couple days the grass underneath is dying. After planting your veggies, I would mulch with whatever is locally available like shredded wood or wood chips. I like the shredded better, it is easier to move around,softer to walk or kneel on, and doesn't float away in a rain. Here in Mississippi, alot of us use pine needles or pine straw as it's called. If you are not planning to plant right away, you can compost in place over your cardboard or newspaper by throwing your veggie scraps and plant waste right on your future garden. Read more about it by searchiing lasagna gardens. You might also want to search about planting in hay or straw bales. Here's one sight: http//www.postpaper.com/haybale.htm
This might esp work for you the first year.

Thanks for the ideas, folks. :-)

I had heard of square foot gardening but didn't realize it had such a following. It's a compelling idea... I just requested the book from my library. One good thing is I could get started sooner, like this year. It does say on their site that you can have any place where water pools after rain, and that's a good description of my plot now. Hence, the reason I was going to mix in some organic material. I don't want to raise them all off the ground.

I should also say that we don't have "red" clay here.. it's more like a dense brown/grey clay... I actually think it's fairly decent stuff but the year of heavy equipment and a year with nothing planted in it compacted it to what it is today.

Luckily, the area is already cleared... just need to decide what to till into it to improve the tilth/drainage... etc.