rich in biodiversity and scenic beauty, a fact appreciated by native West Virginians, who refer to their home as Almost Heaven (from the song "Take Me Home, Country Roads" by John Denver). Before the song, it was known as "The Cog State" (Coal, Oil, and Gas) or "The Mountain State". The underlying rock strata are sandstone, shale, bituminous coal beds, and limestone laid down in a near-shore environment from sediments derived from mountains to the east, in a shallow inland sea on the west. Some beds illustrate a coastal swamp environment, some river delta, and some shallow water. Sea level rose and fell many times during the Mississippian and Pennsylvanian eras, giving a variety of rock strata. The Appalachian Mountains are some of the oldest on earth, having formed more than three hundred million years ago. Climate The climate of West Virginia is generally a humid subtropical climate (Köppen climate classification Cfa, except Dfb at the higher elevations) with warm to hot, humid summers and chilly winters, increasing in severity with elevation. Some southern highland areas also have a mountain temperate climate (Köppen Cfb) where winter temperatures are more moderate and summer temperatures are somewhat cooler. However, the weather is subject in all parts of the state to change. The hardiness zones range from zone 5b in the central Appalachian mountains to zone 7a in the warmest parts of the lowest elevations. In the Eastern Panhandle and the Ohio River Valley, temperatures are warm enough to see and grow subtropical plants such as southern magnolia (Magnolia grandiflora), crepe myrtle, Albizia julibrissin, American sweetgum and even the occasional needle palm and sabal minor. These plants do not thrive as well in other parts of the state. The eastern prickly pear grows well in many portions of the state. Average January temperatures range from around 26 °F (−4 °C) near the Cheat River to 41 °F (5 °C) along sections of the border with Kentucky. July averages range from 67 °F (19 °C) along the North Branch Potomac River to 76 °F (24 °C) in the western part of the state. It is cooler in the mountains than in the lower sections of the state. The highest recorded temperature in the state is at Martinsburg on July 10, 1936, and the lowest recorded temperature in the state is at Lewisburg on December 30, 1917. Annual precipitation ranges from less than in the