We know of these forests because of the splendid sample of fossil seeds, nuts, fruits, leaves, branches, and roots. The Clarno Nutbed is one of the finest fossil plant localities on the planet, with hundreds of species, many new to science, preserved. The Nutbed was deposited in a lake delta and covered with sediment. Other Clarno fossils (mostly leaves and wood) were preserved when huge lahars swept down from nearby volcanoes and covered parts of the forest. Eventually the plant matter became permineralized and today we have a very detailed look at this ancient world.