for those of you who live south of the area where the earth freezes, this is a trench for a footing. It must be 42" below grade in this locale. The cement man needs it to be 6' wide 'cause his men are fat (did I say he didn't show up to place the forms?). Our trench depth varies from 23" to 42" deep because of the natural grade, the transit keeps us on target. The footing will be 10" thick and 20" wide, so I'm told, and I hope to live to see it.