Casey was promoted from Major to Colonel. The next grade is LTCOL, addressed when speaking as Colonel. So his next rank, unless he skipped a grade, would be LTCOL. LTCOL rank insignia are oak leaves. A full Colonel wears an eagle. His dress uniform in the coffin shows him wearing Eagles, a grade too high.
The opening scene is identified as taking place in "Zargos Mountains, Iran"; the correct spelling is "Zagros".