Good day!

I am hoping to find some people with experience to guide me through the first couple of steps in helping me achieve my goal of creating a rather large deck in my backyard. First, my goal is to create a deck in my backyard that will extend to my property line but the problem is that this would entail building the deck on a 30' downward slope. With this being said, I'm fairly sure that I will need permits, and professional plans done up since I live in a danger earthquake zone.

I live in Northridge, CA (i.e. the 1994 Northridge Earthquake of California) so frost is not a concern of mine--I'm more concerned about liquefaction of the soil, natural erosion, etc. My question is this: Where do I begin to uptake this project? I want to do the project myself, at least the parts I can do such as the construction, but I have no idea how to draw up plans or otherwise. Could somebody point me in the right direction?

It starts with an architect who will "design" the structure. S/he will either have engineering skills for this kind of project or will have an engineer handy who will double check science against the art.

Then you will need a general contractor. A general contractor will take the engineered specs and blue prints and put the paper to solid stone/wood/steel/ whatever material is used.

The Contractor will be your liaison to the Building Inspector, will get the proper building permits, will coordinate the heavy equipment, labor, etc.

So where should you really start? At the Building Inspectors office: They usually have all the information you need to get you started on finding the right people to do the work you need. They also keep track of quality professions in the field of construction.

You may be able to do all of the construction yourself, however as tall as this (30' at one end?)is you may have to have pylons/piers sunk deep into the ground in that case you are better off hiring the contractor (GC) who either has a team or hires a subcontractor to drill the pylons, set up the re-bar and do the pouring of concrete (which is can be a real bear at times).

If liquefaction is a problem in your back yard, then those pylons might have to go a bit down.

There are maps on the Net for Liquefaction Hazards usually interactive enough to find your neighborhood to see what the risk is. Failing that the Building Inspectors office will have a good idea, so that makes sense to start there.

there are similar slopes in southeast Alaska. Post and pier is the way to go, but the piers must be sunk a ways. I live on a slope here and while the grade isn't that exteme it does drop about 3' every 12'. I did all the work myself and used piers that don't have to be sunk very far (the pyramid shaped ones you can buy for about $5 apiece).
DvdGStwrt is right, concrete work can be a bear. I buy 80# bags and mix it myself in a 5 gal bucket, hiking the bags on my shoulder down a 200' + dirt driveway. I don't think the tendonitis (?) in my right elbow will ever go away.