A midden is a mound, of varying size and composition, created by animals or human beings. The middens of desert wood rats (Neotoma lepida), also called pack rats, are often constructed around the base of prickly pear and cholla cactus, where they form virtually impregnable fortresses against predators. In addition to bones, fur, teeth, and other collected animal remains, their midden nests include twigs and hardy plant material, as well as found objects, from walnut shells to belt buckles. Some preserved pack-rat middens are large enough and old enough to contain many thousands of years of evolutionary history for a single species—a meadow vole, say—offering scientists an unprecedented record of how a species has changed and evolved, and how its evolution has been affected by climate change. Middens created by human beings comprise all the leftovers from village life—worn out clothing, broken pots and tools, unrepairable toys. In Wind in the Rock, Ann Zwinger writes of an Anasazi midden at the base of Junction Ruin in Grand Gulch, Utah, that produced “pieces of corn cob, soft cotton string, shreds of bark (used for bedding and diapers), turkey feathers” used in making blankets and capes, and yucca ﬁbers, for which the Anasazi had many uses. In her memoir Already Home, Barbara Gates painstakingly describes one of the more than 425 shell mounds found around the rim of San Francisco Bay, writing that these middens were composed mainly of charcoal, ash, and shells—kitchen life.