Vegetable Garden Calendar

I found this on the Homesteading Self Sufficiency Survival Blog (don't read too much into my following that blog), but haven't determined the source.  I'm interested in whether you think it's above or below our 39th parallel.  Down here by the river at 570 feet above sea level, I consider May 1 to be frost-free, but friends on Dan's Mountain and Jersey Mountain add as much as two weeks to that.