Water samples from short-screen monitoring wells installed along a 90-km transect in southwestern Kansas were analyzed for major ions, trace elements, isotopes (H, B, C, N, O, S, Sr), and dissolved gases (He, Ne, N₂, Ar, O₂, CH₄) to evaluate the geochemistry, radiocarbon ages, and paleorecharge conditions in the unconfined central High Plains aquifer. The primary reactions controlling water chemistry were dedolomitization, cation exchange, feldspar weathering, and O₂ reduction and denitrification. Radiocarbon ages adjusted for C mass transfers ranged from <2,600 (¹⁴C) yr B.P. near the water table to 12,800�0 (¹⁴C) yr B.P. at the base of the aquifer, indicating the unconfined central High Plains aquifer contained a stratified sequence of ground water spanning Holocene time. A cross-sectional model of steady-state ground-water flow, calibrated using radiocarbon ages, is consistent with recharge rates ranging from 0.8 mm/yr in areas overlain by loess to 8 mm/yr in areas overlain by dune sand. Paleorecharge temperatures ranged from an average of 15.2�7^oC for the most recently recharged waters to 11.6�4^oC for the oldest waters. The temperature difference between Early and Late Holocene recharge was estimated to be 2.4�7^oC, after taking into account variable recharge elevations. Nitrogen isotope data indicate NO₃ in paleorecharge (average concentration = 193 礛) was derived from a relatively uniform source such as soil N, whereas NO₃ in recent recharge (average concentration = 885 礛) contained N from varying proportions of fertilizer, manure, and soil N. Deep water samples contained components of N₂ derived from atmospheric, denitrification, and deep natural gas sources. Denitrification rates in the aquifer were slow (5񶕭0^-3 mol N L^-1 yr^-1), indicating this process would require >10,000 years to reduce the average NO₃ concentration in recent recharge to the Holocene background concentration.