Packrat Midden. A "midden" or "midden pile" is a fancy name for a trash heap. When ancient people made middens, they left behind the things that archaeologists dig through. From the trash, archaeologists determine how the ancients lived, what they used for tools, and what they ate. When packrats (specifically Desert Woodrats) make midden piles, which are mostly solidified urine, feces, plant material, and bones, biologists can dig through the midden to determine the same things.

Scientists use packrat middens these days to study climate change by excavating the middens and identifying plant fragments in the layers. Different species of plants grow under different climate conditions, so using the plants and carbon-14 dating, scientists determine when the plants were alive, and thereby date the changes in climate. Using midden piles from the Las Vegas area, biologists have determined that much of our desert was covered with singleleaf pinyon pines and Utah juniper trees at the end of the last ice age (about 10,000 years ago). So look for enormous middens and contemplate their age, but leave them alone, and thank the packrats for their contribution to our knowledge of the changing desert ecosystem.