The soil of the ritual mounds (Túmulo No 1 and No 2) at the archaeological site Az-67 in the Azapa Valley, northern Chile, were studied. These monticules (túmulos) are formed by successive layers of vegetables and soil; they were built during the Formative period (1,500 BC500AC) in the area. The archaeological samples of soil were compared to a reference column without evidence of anthropogenic activity. The soluble and silicate fractions of the soil were analyzed with scanning electronic microscopy, inductively coupled plasma with optic emission spectroscopy, and granulometry. The silicate fraction data show that the soil layers of these túmulos are homogeneous and belong to this area, while the soluble fraction suggests a mixture of soils from areas richer in salts with soils poor in salt.