All in all, you're going to have a tough time being self-sufficent here unless you've got a lot of money to build and operate large greenhouses.
I really disagree Don. Granted, greenhouses will obviously extend growing seasons and give you some degree of year-round production, but they are not absolutely necessary. With proper gardening techniques (not requiring massive soil improvements either), one can be completely self-sufficient in *most of* Wyoming. If people follow a simple plan for self-sustained farming, they can provide for their own family quite comfortably. That plan includes short and long-term use root and veggie crops (stored or preserved accordingly), basic protein requirements (chickens, cows, horses, goats, fish, dairy, etc.), and basic grain products (1/2 acre of select grains can provide a family flour for a year). The largest problem with doing this is the amount of work required. It is extremely labor intensive. Additionally, maintenance of seed becomes an issue long-term.
All that said, if one has about 1 - 2 acres of land available for production, they can be food self-sufficient without green houses, even in *most of* Wyoming. I qualify that because the band of Wyoming from Laramie over to Green River is about the worst in the state for any life to exist at all. It would be hardest in that region.
What has not really been covered in this thread, however, is the change in quality of life/lifestyle that will come when people are forced to become self-sufficient. I think the necessary move away from the recreation based life, 9-5 workdays, and drive anywhere/anytime lifestyle will present more of an insurmountable problem than the difficulty of growing one's own food. Most people will not be able to take care of themselves because we, as Americans, have become a nation of soft pussies who want everything without truly earning it for ourselves. Some, like the people on this board, recognize the changes coming and will have little difficulty in making the change - it will still suck but we'll get 'r done. The rest of our society will implode when their cell phones stop working, they can't tweet the color of their latest BM, and their double-chocolate, part-skim, decaf mochachino requires a 4 hour walk under threat of attack, coupled with a $4700 price tag. I think growing food will be a small problem in the greater scheme of things.
*BTW: you can build a 15X48 hoophouse that will withstand WY weather for about $1000-$1500. *Just because I say one doesn't "need" a greenhouse doesn't mean I'm not going to have any!