Possible Clues:

• Cattle drive destination in 'Lonesome Dove'
• Body briefly set up to incorporate new state
• Nato man (anag) — US state
• Grumble after collecting books in a state
• State with the motto 'Oro y plata'
• State that sounds empty when it's been reduced!
• Western state
• State body cut up about end of taxation
• Part of Vermont, an American state
• The Treasure State