The top level or "roof" of the stacks was blanketed with a patchwork array of old solar panels that provided supplemental power to the units below. A bundle of hoses and corrugated tubing snaked up and down the side of each stack, supplying water to each trailer and carrying away sewage (luxuries not available in some of the other stacks scattered around the city). Very little sunlight made it to the bottom level (known as the "floor"). The dark, narrow strips of ground between the stacks were clogged with the skeletons of abandoned cars and trucks, their gas tanks emptied and their exit routes blocked off long ago.