Think of this as the same journey seen from the other end of the segment. The label here is Portal del Inca to Río de la Sal, and the first half of that name is the interesting one. Portal suggests a gateway, a place where the trail passes through a narrowing or a pass and the ground begins to change. Without a signed monument underfoot, the useful thing to say is what the surrounding country does: the Atacama's interior basins rise gradually toward the Andean crest, and the Inca engineers used each step in that rise as a staging post.
Rivers in this part of Chile are rarely rivers in the European sense. The Río de la Sal is a thin ribbon that dries and floods with the season, and the vegetation hugs it tightly: a green seam, some grasses, and then a sudden edge where the desert resumes. Animals know that seam well. You may see vicuña or guanaco on the slopes above, usually lifting their heads together and then deciding you are not worth the effort. Flamingos turn up at the salt lakes higher in this part of the Andes, though not necessarily here.
There is no town on the doorstep. The nearest settlements of any size lie a long way off along the main road, and for supplies you should think of Diego de Almagro, with its fuel, shops and a bed, as your base. Filling up to the brim there and carrying extra is not caution for its own sake; it is simply how the region works. Help, if you need it, is slow to arrive, so tell someone where you are going and treat every unmarked fork as a decision.
The surface is the main thing to understand. Tracks like these are graded in some places and washboarded or sandy in others, and after rare rain a dry wash can turn soft in minutes. Keep your speed honest, look far ahead for the darker patches that mean sand, and give yourself margin on gradients where gravel sits loose. In return you get a line of sight that reaches for dozens of kilometres, a sky that goes properly dark at night, and the odd sense that you are following people who walked here five hundred years ago with far less than a fuel tank to worry about.