Decks, Patios, Porches and Docks - Concrete footings...how deep?

Greetings all...

I just discovered this board, and I am glad that I did.

I am about to replace an aging and decrepit front deck on my cabin. I want to do the whole job myself. The house is 30 years old and the front of the house was never adequately protected from the elements. The deck is about to fall apart.

Here are the issues:
1. the house is on a slope, so the front supports for the front deck are roughly 6 feet tall.
2. The house is in an unincorporated area, so not eveything is up to code. The cement footings that the original support beams are tied into are quite small and look very inadequate.
3. It snows. I have heard that you need to make sure you get below the frost line in order to avoid some sort of upheaval when the ground freezes. Another issue is that the substrate is decomposed granite (I'm at 6000 feet in the San Jacinto Mountains of California, if anyone is familiar with the area), and since it's on a slope, erosion is a serious issue.

So... I want a study deck, and I want it to last. Is there any way to find out just how deep I need to dig to install those footings? This is really the only thing holding me back at this point...

Thanks in advance...

Check with your local Building Department

I've made it as far as the building department. All it says for footings, is how wide they should be based upon the size of the beams, "provided a 12" min depth below undisturbed ground surface."

I read elsewhere to beware of the depth to which the ground freezes. So, does the code mean 12" below the level to which the ground feezes, and if so, how do I figure this depth?

In essence, I think between the erosion issue and the frost, I should be a bit cautious. Also, the majority of Riverside County, for which the codes are written, is low in elevation and mostly desert. The only communities in the mountains are unincorporated, so I also have to wonder if these codes are not suited for the mountainous regions.

thanks for any insight.