Archaeological artifacts are very much affected by the sort of ground in which they are buried.
An object or artifact that survives well in one type of soil does not necessarily survive in another. Just think of the splendid remains of mummies and the many other treasures from ancient Egypt. Artifacts such as human remains, papyrus, wood, and ivory found in Egypt have survived so well because of the hot, dry desert sands, which contain very little moisture and the kinds of tiny micro-organisms that live in damp soil that would eat these things. In North America, only a small part of the wonderful ancient remains have survived over time, because the climate is damp and the soils are full of living micro-organisms that feast on organic remains. Soil also varies in levels of acidity.