An interesting read about Pack Rat middens that date back 50,000 years in excellent condition including DNA, enabling species identification and hence local environmental changes over time. They have also collected items of slaves of the early 1800’s to throw a light on the lives of a caste of people not normally recorded.
>>Pack rats, also known as wood rats, are notorious for collecting an odd assortment of items from their surroundings to make their nests, called middens. Although pack rats are similarly sized to their city-dwelling brown and black rat cousins, they have bushy (not hairless) tails and belong to the genus Neotoma rather than Rattus. These stockpiling rodents tend to only range 100 to 150 feet from their middens, collecting items from about a 50-foot radius. Pack rats will gather everything from plants and branches to insects and bones, which they pack into their middens. While you might not expect such materials to survive for very long, pack rats also have a special trick to conserve their haul: urine.
Pack rats pee all over their nests, and in arid climates (like deserts), the urine crystallizes as it dries. This preserves the items inside the middens, but it also presents a challenge to scientists studying the finds. “They have very highly concentrated urine, and once it crystallizes, it’s rock hard,” says Buffalo State College ecologist Camille Holmgren. “In order to collect middens, we often need a rock hammer and a big boring chisel to hammer away at these things because they’re often cemented to the rocks.”<<
https://www.smithsonianmag.com/science-nature/archaeological-treasures-hidden-rat-nests-180973544/