The soil samples are from a closed-system river basin named Libres-Oriental, located parallel to 18°50' and 19°05' west longitude, and it covers an area of 5250 km². The temporary lagoon, called Laguna del Carmen (LDC), is surrounded by steep mountains, the altitude locally ranges from 2312 to 5765 m. Principal objective: to determine the sorption of the mycotoxin Aflatoxin B₁ (AfB₁), which is a frequent contaminant of corn. The sorption of AfB₁ to samples of LDC may provide an option for its future use. Properties determined: pH, CEC, extractable bases, and mineralogical analysis by x-ray diffraction (XRD), and transmission electron microscopy (TEM) were determined. Bulk samples have a pH=10, mean CEC and extractable bases in cmol/kg are: CEC=65; Ca=38; K=14; Na increases from 63 to 81 and Mg from 10 to 19 with depth of the profile. In coarse clay the results were for mean sorption of AfB₁= 0.117 mol/kg; particle thickness of smectite peak from XRD 6.2 nm. The d-spacing of samples saturated with AfB1 was 1.4 nm and after heat treatment at 245°C it collapsed to 1.3nm. Under the same conditions without AfB1 collapsed to 1.2 nm. Smectite particles from commercial sorbent-bentonites crushed for marketing tend to have complex morphology with irregular shapes and thickness. The clays from LDC have more discrete particles many of which are relatively uniform in thickness. These discrete particles are indicative of crystal growth in a disperse system in contrast to compaction (induration) of typical bentonite rocks. Energy dispersive spectroscopy data suggest the LDC samples contain Mg, in similar amounts to Al, whereas typical bentonites contain much more Al than Mg. Even though there are differences in composition and physical properties the sorption seems to fit the Langmuir model as do good bentonite sorbents of AfB₁.