How does Hal Borland use imagery in When the Legends Die?

Imagery:

He wasn't riding for time or for the crowd. He was riding for himself. And he wasn't riding the bay. He was riding a hurt and a hate, deep inside. The blood drummed in his ears, his teeth ached with the pounding, but he held his rhythm.

He looked at the sky, the blue roundness of the sky, and he looked at the roundness of the aspen trunks. He closed his eyes and sang a silent chant to the roundness of all things, the great roundness of life.