What is symbolic about the landscape that Peewee Cobb flies over?

It is symbolic of a nuclear holocaust that leaves Randy and the people with him in a hopeless predicament.

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As he circled, the sky in the southeast grew light. When the sun touched his wingtips, the sea was still dark below. Then gradually, the shape and colour of sea and earth became plain. He felt entirely alone and apart from this transformation, as if he watched from a separate planet. He checked his map. Far to the east he picked out Mount Carmel, and a river, and beyond were the hills of Megiddo, also called Armageddon. He continued to orbit.

"As he circled, the sky in the southeast grew light. When the sun touched his wingtips, the sea was still dark below. Then gradually, the shape and colour of sea and earth became plain. He felt entirely alone and apart from this transformation, as if he watched from a separate planet. He checked his map. Far to the east he picked out Mount Carmel, and a river, and beyond were the hills of Megiddo, also called Armageddon. He continued to orbit."

The landscape in this section is symbolically dark and grim, but the sunlight brings light and visibility (something he doesn't even notice). This is also the section in which Megiddo is mentioned (a reference to the Biblical Armageddon.