Rebels of the Red Planet by Charles L. Fontenay

The Xanthe Desert stretched red and barren on all sides of the plodding couple, the sands unbroken by the form of plant or stone or any living thing, all the way to the tight horizon of Mars. Above them, the small, glittering sun slid down the copper-hued sky slowly toward the west.

It was remarkable, thought Maya, how smooth and flat the desert looked from the air, and how rough and rolling it was when one had to walk across the packed sand. They had been walking for hours and, despite the gentle gravity of Mars, she was getting very tired.