As long as they don't climb up to you at night.
Much of a muchness. Black basalt gives off heat all night long and is nowhere near cool by dawn. And this is after the zombies had hiked across a waterless desert.
Years ago, when the government was contemplating very long term storage of high grade nuclear waste, perhaps 500 or a thousand years in the future, they seriously considered covering the site with a mountain of black basalt boulders. Only very slowly eroding, it would make treasure hunting on the site extremely hard.