It's very American, too, the notion that you can turn your back on the old country and ways and go to the new world and start over making your own rules, laws, customs.
Before the Pilgrim Father landed they saw themselves as about to become a city on a hill, a beacon to the rest of mankind - ironically Jack and Ennis turn their hill into a little world of their own, with their own rules, but keep it hidden from everyone, so that in the end, as Jack says, all they have is Brokeback Mountain.
When I looked at that scene again, I thought of "For God's sake let us sit upon the ground
And tell sad stories of the deaths of kings,"
but also of the idea of measuring one's length on the ground, six feet of earth, which is all you're going to have in the end. For me there was a lot of foreshadowing in this scene.