||This study presents a late Holocene fire, vegetation, and climate history from ~2500 to 740 cal yr BP of Ciénega de San Bernardino, a desert wetland in southwestern North America. A high resolution multiple sedimentary proxy approach was used in conjunction with solid chronological control to determine the environmental history of Ciénega de San Bernardino, a wetland on the international border between extreme southeastern Arizona, United States, and northeastern Sonora, Mexico. The combined sedimentary proxies of macroscopic charcoal particles, pollen, loss-on-ignition, magnetic susceptibility, grain size analysis, and sound AMS radiocarbon dating was used to reconstruct the pre-European environmental history of this wetland. Results reflect a relatively stable wetland ecosystem within a fluctuating but continuously depositional environment for the approximately 1800 year record. Sediment proxies show this ecosystem to be sensitive enough to record changes in surface hydrology, vegetation, and fire regime. Of special interest is a rapid, large, and sustained change in the fire regime of this site which temporally coincides with the Medieval Climate Anomaly. This study shows that these perennially wet ecosystems are effective and important archives of past environmental conditions and change. The information presented here can be used to inform land managers of the pre-European settlement environmental conditions in southwestern lowland deserts, and the likely response of these systems to future climate change.