The Neopluvial was a phase of wetter and colder climate that occurred during the late Holocene in the Western United States.
[14] Ice patches in the Beartooth Mountains[15] and glaciers grew in the Sierra Nevada,[16] sagebrush steppe, green Mormon tea and other vegetation expanded in the Great Salt Lake region,[17] marshes expanded in the central and northern Great Basin,[18] mammal communities in the Lake Bonneville basin changed with the return of the long-tailed pocket mouse, the Great Basin pocket mouse and the Western harvest mouse to sites where they were not present before and increased abundances of even-toed ungulates,[19] and tree lines dropped, with the lower limit of wooden vegetation penetrating into deserts.
[20] Counterintuitively, higher tree line elevations in the Lake Bonneville area occurred during the Neopluvial, which may indicate warmer summers.
[22] In the Owens Valley region, during the Neopluvial the human population became more sedentary and trans-Sierra Nevada trade became established ("Newberry"/"Middle Archaic Period").
[27] This cooling is primarily explained by steadily declining summer insolation, though synchronous patterns in hydrological responses at sub-millennial scales may be linked to atmospheric circulation shifts driven by factors such as internal variability in ocean-atmosphere teleconnections.