Fig. 3: The proportion of Anthropocene (since 1953), Holocene, and Pleistocene groundwater at the depth zone used for public supply in 21 Principal Aquifers in the continental United States.

Blue bars represent Anthropocene proportions, yellow bars represent Holocene proportions, and red bars represent Pleistocene proportions. The Principal Aquifers and their abbreviations are defined in Fig. 1.