Historical clue formulations

• Texas city on Route 66 — 2019-01-12
• City with the slogan "Step Into the Real Texas" — 2013-04-11
• City mentioned in "Route 66" — 2010-07-31
• Panhandle city — 2010-03-25
• Texas panhandle city — 2009-01-29
• Home of the Cadillac Ranch — 2008-10-05
• Title city in a 1983 George Strait hit — 2007-06-30
• Helium Capital of the World — 2003-06-27
• City that's the title of an Emmylou Harris song — 2000-07-15
• Big cattle ranching center — 2000-05-13
• Texas metropolis — 1995-05-18
• Texas town — 1994-05-13