Question

If I were in Your place, I would turn to the community: "Please, everybody come in, in shifts, and dig the hole lot from end to end, two spades deep(trench rotation) and get all the rubbish out: rocks go into one corner(they may be needed later for a dry wall or such) the litter into another corner, which remains accessible for future disposing of the pile. While You come in, everybody brings whatever organic material he/she can get his/her hands on for composting on site." The water issue can possibly be resolved by carrying water in, again done by the community in shifts, along with mulching. Whether this is possible in Your climate or not will be best known by local gardeners in Your area. Everybody knows who's on shift at any given time, so slapping for neglecting the garden would also be done by the community. Also, before I start I would like to have some kind of commitment from the owner for at least a few years of usage. After all You are turning a desert into a garden and should be allowed to enjoy it for some time in return of Your effort. Of course, all the above may or may not work, but it surely would prevent me from becoming a one person community garden, i.e. a garden slave.

If you have a way to collect rainwater, that might be an alternative for the watering solution. Also, you could consider container gardening. It's easier to start, you won't need to dig up the ground, but containers dry out faster and usually need more watering than plants in the ground. If you can get a composting system and/or worm bins going, those will help improve the soil tremendously. You might be able to get together with a nearby school, group or organization, museum, home center, something that can help you spread the word, bring people in to help, maybe educate kids as part of a school or afterschool project, maybe even get donations of materials and/or labor. Ask the property owner. They may very likely have some connections that could both help you, and possibly themselves too, using publicity to their benefit for their business? You never know; things have a way of working out in unexpected, cool ways...Good luck with this! I hope you can get it going well. There are some tips in this post I did for how to start your garden for almost free: http://kgi.org/blog/alina/how-start-your-own-garden-almost-free