We are given that the height of the flag (opposite side) is 6 meters, and the length of the shadow (adjacent side) is \( 2\sqrt{3} \) meters. The angle of elevation \( \theta \) can be found using the tangent function:
\[
\tan(\theta) = \frac{\text{opposite}}{\text{adjacent}} = \frac{6}{2\sqrt{3}} = \frac{3}{\sqrt{3}} = \sqrt{3}.
\]
Thus, \( \theta = 60^\circ \), as \( \tan(60^\circ) = \sqrt{3} \).