The presence of Cs-137 was detected in soil samples from thirteen sites along parallel 33 degrees,3 S at altitudes in the range from 900 to 1800 masl along the Maipo River canyon, near Santiago, the Chilean capital city. Gamma spectroscopic analyses performed to the samples allowed identification of radionuclides emitted in the decay processes of the natural precursors U-238, Th-239 together with primordial K-40. Concentrations of Cs-137 relative to K-40 showed significant variations.