Here's another shot. You can get a feeling of the depth in this one. 6' is way down there! Our frost line is only around 42", but I've heard that in some winters it can go lower with low snowcover.
This is how far I went on day 1. I had a few visitors and took lots of breaks to get out of the heat, but I think 120' of 6' trench for a day is pretty good. It's a 12" trench for the most part.