that the unreal feeling of the landscape was more than a creation of the dust; it was the light. It came from the distant sun, frail, refracted by the dust and other elements in the atmosphere. That explained the darkness of the planet, as if it existed in twilight, but it didn't explain an odd, fine, threadlike quality to the light that had not come through in the probe's transmissions, as if the light had been filtered through a polarizing lens, or strained into a shifting, fibrous curtain in the dusk. As Anna rounded the side of the crawler, she saw the low, trailing fragments of the smaller mountain range up close.
The black rock of these dust-weathered remnants erupted from the reddish-brown stone of the landscape in a series of rocky outcroppings. Dunes of sand and dust had formed along their base. Near the end of these mountains, beside an outcropping of black stone approximately fifty feet high, the crawler had stopped. Anna moved away from the crawler toward the outcropping, climbing the slight dune. Gradually the sand gave way to the dark shards of rock that formed the talus. There, before her, lay the cave mouth, its shadow a darker black than the blackness surrounding it, an opening seventeen feet across and fourteen feet high.
Anna turned on her flashlight and aimed it at the edges of the opening. The flashlight illuminated a beam of blowing dust and, faintly, the ragged edges of the rock. The presence of the mice in the cave suggested it had once been inhabited, or at least visited. They didn't have enough data yet to know during what period that had been true, but she hoped to find out soon. In general caves were used for shelter, for storage, for mining, for strategic location, as holy sites, or as tombs.
Most often cave activity was focused around