Turn the crank so the right arm is pointed upward. This will allow you to snake the left side of the crank out of the frame. Sometimes it helps to have a screwdriver handy to push the bearing cages out of the way.

As FB said- you have a one-piece "Ashtabula" crank: http://sheldonbrown.com/opc.html .

I overhauled hundreds of these in my bike shop days. Once you get it oriented correctly, it should just about fall out.