Other ingredients that go into soil, like volcanic ash, lake silt, dune sand and glacial gravels, are carried around by water, wind or ice. In warm, moist climates like western Oregon, rocks and minerals break down rather quickly. The roots of large plants help break rocks, and their channels provide pathways for water and air. Large burrowing animals, earthworms, insects and microscopic worms called nematodes help mix particles. The topography, or position of the land, also is important.
Rain runs off hillsides, so they're dryer and soil forms slowly.
But the water collects at the bottom of hillsides, taking with it particles and organisms that help soil form more quickly. Last, making soil takes a long time. Many of Oregon's soils started forming during the ice ages and were placed where they are now, over thousands of years, by wind and water. A rock, a lava flow or a wind-swept hill we see today may be the soil under children we can't even imagine. Sitting atop a core of rock, the inner earth, Oregon's soil generally ranges from a depth of a few inches to 10 feet, but in some spots it's much, much deeper.