The Oregon Coast Range is divided into three separate sections: North, Central, and South. In the south is the oldest portion of the range with formation beginning in the Paleocene era with the Roseburg volcanics, while the newest section is the northernmost portion formed first with the Siletz River Volcanics. The Central and Northern sections contain more sedimentary rocks from the mud, silt, sand, and other volcanic debris than the lower Southern section. Also, the Oregon Coast Range is home to over 50 mammal species, over 100 species of birds, and nearly 30 reptile or amphibian species that spent significant portions of their life cycle in the mountains.