Valle del Arcoiris, the Rainbow Valley, is a quieter Atacama excursion where the desert changes colour in bands of red, white, green, grey, and ochre. The colours come from mineral-rich clays and rocks in the Domeyko range, and the best moments are in angled light when the ridges stop looking dusty and start looking painted.
Most visits combine the valley with the petroglyphs around Yerbas Buenas, which gives the trip a welcome human layer as well as geology. It is far enough from San Pedro that you will want a tour or your own vehicle, but it is a good counterpoint to the busier Valle de la Luna circuit.