One of the most polluted areas in Chile is the Ventanas Industrial Area (VIA; 32.74°S / 71.48°W), which started in 1958 and today comprises around 16 industries in an area of ca. 4 km2. A lack of consistent long-term instrumental records precludes assessing the history of contamination in the area and also limits the evaluation of mitigation actions taken since the late 1980s. Here, we use dendrochemistry as an environmental proxy to analyze environmental changes over several decades at the VIA. We present chemical measurements of tree rings from planted, exotic Cupressus macrocarpa growing near the VIA with 4-year resolution over a period of 52 years (1960–2011). These data provide unprecedented information on regional anthropogenic pollution and are compared with a tree-ring elemental record of 48 years (1964–2011) from the Isla Negra (INE) control site not exposed to VIA emissions. For the 48 years of overlap between both sites, higher concentrations of Zn, V, Co, Cd, Ag, Fe, Cr, and Al were especially registered after the year 2000 at VIA compared to INE for the periods under study. Concentrations of Pb, Cu, As, Fe, Mo, Cr, and Zn increased through time, particularly over the period 1980–1990. Decontamination plans activated in 1992 appear to have had a positive effect on the amount of some elements, but the chemical concentration in the tree rings suggest continued accumulation of pollutants in the environment. Only after several years of implementation of the mitigation measures have some elements tended to decrease in concentration, especially at the end of the evaluated period. Dendrochemistry is a useful tool to provide a long-term perspective of the dynamics of trace metal pollution and represents a powerful approach to monitor air quality variability to extend the instrumental records back in time.