Paleontology and geology
During the Silurian, the western edge of North America was still underwater. Tabulate corals and stromatoporoids (sponge-like animals with calcareous skeletons) dominated the reef communities that were built up in shallow, warm waters on banks and shoals. These warm waters were also teeming with brachiopods, cephalopods, gastropods, bivalves, and crinoids. Although not shown on this map, Silurian sandstones, shales, conglomerates, cherts, dolostones, and some altered sedimentary rocks can be found in the Northern Sierra Nevada, White Mountains, Inyo Range, and places near Death Valley.