Amarillo ) is the 14th-largest city in the state of Texas, the largest in the Texas Panhandle, and the seat of Potter County. A portion of the city extends into Randall County. The population was 173,627 at the 2000 census. The Amarillo metropolitan area has an estimated population of 236,113 in four counties. In July 2009, the population was estimated at 189,389.Amarillo, originally named Oneida, is situated in the Llano Estacado region. The availability of the railroad and freight service provided by the Fort Worth and Denver City Railroad contributed to the city's growth as a cattle marketing center in the late 19th century. Amarillo is the regional economic center for the Texas Panhandle, and is economically important to Eastern New Mexico and the Oklahoma Panhandle.The city was once the self-proclaimed "Helium Capital of the World" for having one of the country's most productive helium fields. The city is also known as "The Yellow Rose of Texas" (as the city takes its name from the Spanish word for yellow), and most recently "Rotor City, USA" for its V-22 Osprey hybrid aircraft assembly plant. Amarillo operates one of the largest meat packing areas in the United States. Pantex, the only nuclear weapons assembly and disassembly facility in the country, is also a major employer. The attractions Cadillac Ranch and Big Texan Steak Ranch were located on the former U.S. Highway 66, which passes through the city.