At the top is her egg case, and even it is carefully decorated with bits of debris. The core of the string is a dense tangle of various insect parts, plant bits, and who knows what else. This species is the Sanford & Son of the spider world. And there, at the bottom of the trashline, is our spider, looking all the world like part of the trash.
Why do trashline orbweavers build mini landfills? I don't know. Perhaps to better conceal themselves, both from would be predators and prey. And perhaps the string of trash lures flies or other scavengers, who then get caught up in the nearly invisible orb web.
This is a very common spider and if you keep a watch out you're certain to see one sooner than later.