In the diagram below, line $AB$ is parallel to line $CD$. The angle $ heta$ indicated in the diagram is formed between line $AB$ and a transversal line $EF$. If $ heta = 60$ degrees, what is the measure of the corresponding angle formed on line $CD$ by the transversal line $EF$?
Note: Corresponding angles are formed when a transversal intersects two parallel lines. They are equal in measure.