Paleo-climate of the Snake River Plain

[1] Researchers Smith & Patterson analyzed sediment samples from the western Plain's Chalk Hills Formation and found the fossilized inner-ear bones (otoliths) of sunfish to contain hints about the region's climate past.

[3] Sediment samples taken from a site near Bruneau, Idaho retrieved pollen records for the purpose of analyzing the shift in vegetation proportions at the Pliocene-Pleistocene transition.

[3] The steady decline of pine and spruce species was found to be evident as early as the beginning of the Pliocene (represented by the region's Glenns Ferry formation).

[3] As pollen records marched forward through time, it also become evident that sagebrush (Artemisia) and chenopods (regional species belonging to the families Chenopodiaceae and Amaranthaceae) were increasing in frequency near the Bruneau site.

[3] With glaciation comes drier and colder atmospheric circulation which may help to explain the downfall of the conifer woodland at low elevations of the Snake River Plain.

[4] The position of these glaciers diverted the Pacific westerlies, which are and have been the dominant source of atmospheric moisture for the Plain, and introduced dry easterlies into the region.

[4] A study published in 2008 reported the climate estimations described above with reference to several δ18O and δ2H isotope measurements from four groundwater systems in the Boise, Idaho area.

[5][6][7][8] The drying trend observed in the Pleistocene pollen records at the Bruneau site continued throughout the last major glaciation of North America and into the current interglacial period.

[7][8] Sediment cores from Wyoming's Yellowstone Lake and carbon-dated bison remains found in lava tubes on the eastern Plain have helped to illustrate this dry history.

Yellowstone Lake serves as the main water source for the Columbia-Snake drainage system and thus provides context for the Plain's hydrologic history.