Not promising at all: deeply compacted, infused with hydrocarbons and other potentially toxic materials. Is the material sticky clay or something else?

Sorry, but like marshall, I wouldn't touch this for food growing with a 10 foot pole. Turn it into a flower bed if you wish but not food.

There have several discussions on how to salvage soil contaminated such as this over on the Soil, Compost & Mulch forum here (I've linked several of them below for you) and the consensus is - pass on it.

Yes, there are soil tests available - your local county extension office for one - but they will only test for contaminates for a fee. It's a modest one but a fee none the less because their position is the same - pass on it.

As you have already discovered - it only gets worse the deeper you dig so even raised beds over the area wouldn't be safe for food crops.

Sorry, I know it isn't what you want to hear. Good luck finding a different site.

Dave

Here is a link that might be useful: Contaminated soil discussions...

Hire someone with a tractor to come in with a turnning plow, and turn deep and cut.Make sure you know where fill , water, and power lines are before you dig. Then do a soil sample, and go from there as to the soil condition, and what needs to be added.
Sounds like from the many years of heavy weight being on the soil it is compacted.

I'm reading that when you say that it only gets worse the deeper you go, that you are talking about the texture of the soil, not contamination, which you have already stated as only an unknown possibility. Is this correct?

Convince your freind to put out a few bucks for testing before making any assumptions about contamination.

Then turn around and seriously re-think raised beds. Your time - and theirs - has value. And the time and effort you are putting into digging up the existing soil seems to have a greater cost than the materials for a raised bed. If money is really a serious issue for your freind, look into lasagna gardening. It may take a year to collect enough materials for the bed, but I am sure your freind does not want you to kill yourself over a garden. Afterall, you said you would help - not make this a no-cost no-effort project for them.

As for fruit trees, I think GW has a forum or two for trees. Maybe you should direct that question there.
Kay.

Have the ground tested for contaminants...hazardous materials remediation is very expensive. If your soil ISN'T contaminated, then cover the hardpacked area deeply with compost and manure (atleast 6")...let it sit for about a year or so and have someone plow it in fall. after plowing reapply compost and manure leave it for the winter, plow and till it again in spring test fo PH and etc and plant. then in fall apply the layer of compost and manure again. it may take a few years but it will eventually give you workable ground.

My 1st garden at our farm was similar to your predicament. the hard red VA clay had been packed so tightly the first time I tried to plow it the plow wouldn't even bite. It was like trying to plow a paved road. so I gave up and just piled manure on it about a foot deep. that fall the plow made it down 4". the next spring it made it down about 8". 2 years later the plow would run to it's full depth and the soil was already turning to a rich brown.

Nothing that you can do here is going to be quick, cheap or easy.

There is no way around testing before you continue. None. And there's no way you're going to be planting much this year. I think you'd better do it right, or not at all.

Call your local Cooperative Extension Service/Master Gardener Program and ask who does this kind of testing locally. (Shipping soil can get expensive if they want a quart or so at a time.) Explain what you want, don't just ask for a soil test.

Then explain again to the test lab exactly what you've got, and what you're trying to do. Since it was used for auto and truck parking, ASK what tests they would recommend for the substances associated with vehicles. Your main contaminants are probably petroleum products, coolants, and maybe lead, but there could be others.

Once you have your test results in hand, call your Master Gardeners again. Ask if they have a list of plants that you could plant that would draw the contaminants from the soil. These plants would be cut down, collected and taken to the local landfill (NOT to be used as mulch -- they're toxic).

Ask if some of these contaminants CANNOT be collected this way.

If the plants will work, ask how many times you are likely to have to do this. I'm sure that they would suggest more tests after a certain number of plantings. You live in Calif, so you might be able to get two or more plantings in by next spring.

I have read that petroleum hydrocarbons and lead can be absorbed by certain plants. Radiator coolants can contain heavy metals, and I don't know about them.

If you have trouble finding answers, you might call the local Environmental Protection Agency for recommendations.

If the answers you get indicate that you can't clean the soil well enough with plants to grow food, the only other way that I know about is to go in with heavy equipment and dig out a couple of feet of soil, and replace it with noncontaminated soil.

None of this is cheap. If your friend is trying to grow vegetables to save money, the best bet will probably be to find a nearby patch of decent land (vacant lot attached to a homeowner's property might be best) and make an offer to the owner to keep the weeds down, then your friend grows the vegetables and shares with the property owner. Make sure that water can be used on the property, or it's worthless. Just make sure that THEIR land wasn't used as a dump.

Sue

Here is a link that might be useful: Alameda County Master Gardener program

Contact the UC Davis agriculture extension and ask them about sampling the soil. I'd do that before I did anything else.

Here is a link that might be useful: UC Davis Master Gardeners