The Snowy River formation, located in a recently discovered passage in Fort Stanton Cave, New Mexico, may be the world’s longest continuous cave deposit. The formation is composed of white calcite that coats the floor of the Snowy River passage, and currently extends >7 km with its southern terminus still undefined. Core samples collected from the Snowy River deposit reveal a laminated internal structure, indicating episodic deposition of sub-millimeter scale calcite laminae during periods when the passage stream is activated. The age of the basal layer has been determined to be only 820 ± 120 years old, suggesting an abrupt change in climatic or hydrochemical conditions within the past millennium. Since its discovery, the Snowy River passage has experienced three documented periods of streamflow. During each episode, a thin layer of new calcite was deposited. Data loggers indicate an abrupt (~1 week) disappearance of floodwaters in December, 2008, suggesting a point source of recharge such as a losing stream or subterranean pool. Initial precipitation of the Snowy River deposit may correlate to a transition from perrenial streamflow in the cave to ephemeral conditions ~800 years ago due to changes in either climatic conditions or source water input |