Sedimentary Rock Sedimentary Rocks Used with permission of Tammy Peyton, Rock Hounds web editor. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.
Sedimentary rocks are extremely common throughout Iowa.
It is also the type of rock that fossils are most commonly found. The Iowa Geological Survey Bureau has an excellent summary of some of Iowa's most common fossils .