How does Douglas Preston use imagery in Thunderhead?

Imagery:

"An envelope lay in the dirt, and she grabbed it. As she turned to step back into the truck, the headlights caught the front of the envelope. Nora froze for a moment, gasping in surprise."

"'Ever hear of Coronado, the Spanish explorer? He came into the Southwest in 1540, looking for the Seven Cities of Gold. A friar had gone north years before, looking for souls to save, and he returned with a huge, drilled emerald crystal and stories of lost cities. But when Coronado himself came northward, he found only the mud pueblos of the Indian tribes of New Mexico, none of whom had gold or wealth. But at a place called Cicuye, the Indians told him about a city of priests, called Quivira, where they ate from plates of gold and drank from golden goblets. Or course, this drove Coronado and his men into a frenzy.'"

"As they moved away, Holroyd gave a shout. He had walked around to the side of the rock nearest the entrance to the slot canyon. Now he pointed to a much fresher inscription, scraped into the rock with a penknife. As Nora stared at it, she felt her cheeks begin to burn. Still staring, she knelt beside the stone, fingers slowly tracing the narrow grooves that spelled out P.K. 1983."