Considering the accelerating expansion of warehouses and distribution centers (W&DCs) in California, understanding their fossil fuel-derived carbon dioxide (ffCO₂) emissions is critical to achieve California’s carbon neutrality goals. This study developed urban tree-ring records of radiocarbon (¹⁴C) to isolate ffCO₂ enhancements within a W&DC cluster and in the urban background of the Southern California’s Inland Empire, a region of concentrated W&DC expansion. Our results reveal a period of higher ffCO₂ concentrations before 1984, followed by a sharp decline aligning with the implementation of stringent emissions regulations. Subsequent urban emissions increased at a rate matching local population increases. Large ffCO₂ enhancements above the urban background exist within the W&DC cluster, likely resulting from idling trucks. Our results establish the effectiveness of tree-ring ¹⁴C records in studying urban emissions sources, which will be critical in developing emissions regulations specific to localized urban contexts.