Arlene is talking about a local "make out" place at the start of the book:
The woods, mostly scrub and loblolly pine with a few sycamore and oak trees, ended on the hilltop. There was a little grassy clearing where you could spread a blanket and get on with it. The clearing ended in a track of gravel at the lip, and where the hill started its descent on the other side, the heaps began.
"Heaps" was our name for kudzu, a fast-spreading vine that climbed anything it could find and turned it into a shaggy, amorphous mound. The heaps had eaten the woods in the pit at the center of the ring of hills, creeping over the ground, coating the trees. They formed piles and climbed up themselves when nothing else was offered. In some places they loomed up higher than the hilltops. Roach Country, Clarice called it. Roaches love to nest in kudzu.
I found the photo at this website - kudzu is a really scary plant! Be sure to check out the photos in the Kud - Zoo!