Thirteen-Year Cesium-137 Distribution Environmental Analysis in an Undisturbed Area

137Cs activity concentration in soil was analyzed yearly for 13 years (2010–2022) in an undisturbed area in Mexico. The temporal variation at 17 sampling points is consistent with the natural radioactive decrease of 137Cs, excluding increased activity concentration detected after the Fukushima accident at 4 sampling points. Geospatial analysis was permitted to obtain 137Cs activity concentration distributions for each year. The highest 137Cs activity concentration was found at higher topography levels and close to intermittent water streams: 87.1 ± 5.5 Bq kg−1 for the year 2011, which increased to 135.5 ± 14.5 Bq kg−1 for the year 2013, and then 137Cs decreased down to 46.4 ± 4.0 Bq kg−1 by the year 2022. The lowest 137Cs activity concentration was in the range of 0.6 ± 0.1 Bq kg−1 to 13.5 ± 1.0 Bq kg−1 at the points far from the undisturbed area, probably due to anthropogenic activities.