The late Paleozoic mountains collapsed as rifting in Jurassic time began to open the Gulf of Mexico. Pangea began to break up in the Triassic but seafloor spreading to form the Gulf of Mexico occurred only in the mid and late Jurassic. The shoreline shifted again to the eastern margin of the state and the Gulf of Mexico passive margin began to form. Today there are 9 miles (14 km) to 12 miles (19 km) of sediments buried beneath the Texas continental shelf and a large proportion of remaining US oil reserves are to be found here. At the start of its formation, the incipient Gulf of Mexico basin was restricted and seawater often evaporatedcompletely to form thick evaporite deposits of Jurassic age. These salt deposits have buoyantly risen up through the passive margin sediments to form salt dome diapirs, commonly found in East Texas, along the Gulf coast.
East Texas outcrops consist of Cretaceous and Paleogene sediments with contain important deposits of Eocenelignite. Oil is found in the Mississippian ad Pennsylvanian sediments in the north, Permian sediments in the west, Cretaceous sediments in the east, and along the Gulf coast and out on the Texas continental shelf. Oligocene volcanic rocks are found in far west Texas, in the Big Bend area. A blanket of Miocene sediments known as the Ogallala formation in the western high plains region is an important aquifer. Texas has no active or dormant volcanoes and few earthquakes, being situated far from an active plate tectonic boundary.
Main article: Climate of Texas
2004 Christmas Eve snowstorm in South Texas
The large size of Texas and its location at the intersection of several climate zones gives the state highly variable weather. In general, though, there are three main climate zones: the humid subtropical climate (Koppen Cfa) of the eastern half of Texas, the temperate semi-arid (Koppen BSk) steppe climate of the northwestern part, including the Panhandle, and the subtropical steppe climate (nearly an arid desert climate, Koppen BSh) of the southern parts of West Texas, particularly around El Paso.
The Panhandle of the state is colder in winter than North Texas, while the Gulf Coast has mild winters. Texas has wide variations in precipitation patterns. El Paso, on the western end of the state, averages as little as 8 inches (200 mm) of annual rainfall while Houston, on the southeast Texas averages as much as 54 inches (1,400 mm) per year. Dallas in the North Central region averages a more moderate 37 inches (940 mm) per year. Snowfall often falls in the winter months in the north. Maximum temperatures in the summer months average from the 80s °F (26 °C) in the mountains of West Texas and on Galveston Island to around 100 °F (38 °C) in the Rio Grande Valley. Nighttime summer temperatures range from the upper 50s °F (14 °C) in the West Texas mountains to 80 °F (27 °C) in Galveston.
Thunderstorms are very common in Texas, especially the eastern and northern portion of the state. Texas also experiences the highest number of tornadoes out of every state in the Union, with an average of around 139 a year. Although these tend to strike most frequently in North Texas and the Panhandle, every part of the state is subject to these violent storms. Tornadoes occur mostly between the months of April-July but may strike at any time of the year.
Texas emits the most greenhouse gases out of any state. The state's annual carbon dioxide emissions are nearly 1.5 trillion pounds (680 billion kg). Texas would be the world's seventh-largest producer of greenhouse gases if it were its own country. Much of the greenhouse gas emissions come from the state's refining and manufacturing industries which provide the bulk of the United States's petroleum and plastics.
See also: Catastrophic Texas Hurricanes since 1900
Main article: Demographics of Texas
Texas Population Density Map
As of 2006, the state has an estimated population of 23,507,783, an increase of 579,275 (2.5%) from the prior year and an increase of 2,655,993 (12.7%) since the year 2000. Texas has seen an increase in population in all three subcategories-natural (births less deaths), net immigration, and net migration. The natural increase since the last census was 1,389,275 people (2,351,909 births minus 962,634 deaths), immigration from outside the United States resulted in a net increase of 801,576 people, and migration within the country produced a net increase of 451,910 people. The state passed New York in the 1990s to become the second-largest U.S. state in population.
As of 2004, the state has 3.5 million foreign-born residents (15.6 percent of the state population), of which an estimated 1.2 million are illegal immigrants (illegal immigrants account for more than one-third of the foreign-born population in Texas and 5.4 percent of the total state population).
Race and ethnic origins
The annual Houston International Festival spotlights a different culture each year
As of the 2005 US Census estimates, the racial distribution in Texas are as follows: 84.14% White; 12.09% African American or African; 3.62% Asian; 0.17% Native Hawaiian or Pacific Islander; and 1.1% American Indian or Alaskan Native. Persons of Hispanic origin accounted for 35.31 percent of the population and may be of any race. Texas is one of four majority-minority states.
The largest reported ancestry groups in Texas include: Mexican (25.3%), German (10.9%), African American (10.5%), English (7.2%), and Scots-Irish (7.2%). Descendants from some of these ancestry groups are underreported.
Much of east, central, and north Texas is inhabited by white Protestant heritage, primarily descended from ancestors from Great Britain and Ireland. Much of central and southeast-central Texas is inhabited by whites of German descent. African Americans, who historically made up one-third of the state population, are concentrated in those parts of East Texas where the cotton plantation culture was most prominent prior to the American Civil War, as well as in Dallas and Houston.
Other population groups in Texas also exhibit great diversity. Frontier Texas saw settlements of Germans, particularly in Fredericksburg and New Braunfels. After the European revolutions of 1848, German, Polish, Swedish, Norwegian, Czech and French immigration grew, and continued until World War I. The influence of the diverse