Possible Clues:

• Part of 15-Across (Abbr.)
• Gore-___ (waterproof fabric)
• Ritter of country music
• Handle on the range?
• "Oedipus __" : P.D.Q. Bach western-themed parody
• 'Oedipus __' : P.D.Q. Bach western-themed parody
• Large state, for short
• Classic cowboy nickname
• It borders Mex
• Apt nickname for a Dallas cowboy