Western United States

===Geology===
Plains make up much of the eastern portion of the West, underlain with sedimentary rock from the Upper [[Paleozoic]], [[Mesozoic]], and [[Cenozoic]] eras. The [[Rocky Mountains]] expose igneous and metamorphic rock both from the [[Precambrian]] and from the [[Phanerozoic]] eon. The Inter-mountain States and [[Pacific Northwest]] have huge expanses of volcanic rock from the [[Cenozoic]] era. [[Salt pan (geology)|Salt flats]] and salt lakes reveal a time when the great inland seas covered much of what is now the West.

The Pacific states are the most geologically active areas in the United States. [[Earthquake]]s cause damage every few to several years in [[California]]. While the [[Pacific states]] are the most volcanically active areas, extinct [[volcano]]es and lava flows are found throughout most of the West.