Proper depth for deck footing in Southern Alberta?
 

4' for concrete pillars? Thanks.

depends on soil and geography

my uncle was told to go 40' on the edge of a ravine. he appealed it i'm not sure what's happening now

Depends what the municipality wants.

Typically, unless the deck is under 3' high, you will need 4' piles on pad footings.

http://www.lethbridge.ca/Doing-Busin...20Template.pdf

A very general guideline if your deck can tolerate some vertical movement due to frost heaving would be below the frost depth which is about 1.5 m in you area so about 6 feet.
If the structure cannot tolerate any vertical movement then you would need to go about double that - 10 to 12 feet with a piling system.

There may be a valid reason for that. Improper excavation or construction of foundations at the crest of or one the slope could result in slope failure (slide), meaning you wake up one day and your house is at the bottom of the ravine.
I would not construct on that situation without having a slope stability analysis and construction recommendations signed and stamped by a professional geotechnical engineer.

I went with engineered screw piles to 10 ft. I figured, did I really want to deal with a deck that moves around after a few years? At 10 ft, it should be rock solid for a LONG time.

I wouldn't do anything less than 4' and 6-8' would be even better.

i get it and the foundation pilings are all up to snuff. but the deck piling? if there's a land slide and it leaves your deck or takes your deck and the land around your house i'm sure the difference is rather unsubstantial. but hey i'm cheap and i'm sure it runs in the family