The study of extreme evaporitic environments is a subject of increasing interest in sedimentary petrology and planetary geology. We report here the evaporitic precipitation in the shallow, small lakes (puquı ́os) at the Salar de Llamara (Atacama Desert, northern Chile). We have used a combination of in situ/laboratory/modeling methodologies allowing for the definition of a detailed, in-depth model for the sequence of evaporitic precipitation in the puquı ́os. The in situ measurements in these ponds reveal that brines are density-stratified with important gradients in salinity, temperature, and other properties of the solution (pH, oxidation/reduction potential, and dissolved oxygen). These vertical gradients, along with the lateral and seasonal variations, are the main factors of chemical variability controlling the precipitation processes. The evaporation of these brines drives the chemical evolution of the different ions and produces two distinct mineral assemblages: (i) large structures made of millimetric to centrimetric-size crystals of gypsum often forming thrombolite-like or stromatolite-like morphologies in the ponds and (ii) salt crusts made of mainly gypsum, eugsterite, halite, and thenardite surrounding the ponds. Evaporation experiments in the laboratory monitored by in situ X-ray diffraction and optical videomicroscopy reveal a precipitation sequence in accordance with field observations but distinct from the thermodynamically predicted precipitation. The actual formation of eugsterite, rather than glauberite, and the observed delay in gypsum dissolution are explained using kinetic evaporation models.