Lolo Pass

Warmer average temperatures prevent the buildup of snowpack that historically lasted through the summer and fall, making it difficult for the expedition to travel through the mountains in 1805 and 1806. This photograph shows the lack of snow in the Lolo Pass area in June 2010.

Roger Peterson, USFS

On September 13, 1805, following a local Shoshone guide they called Old Toby, the expedition crossed the Bitterroot Range through Lolo Pass. With rough terrain and falling snow, the trail through the mountains cost them eleven days and much hardship. Clark wrote that he was “as wet and cold in every part as I ever was in my life.” On the return journey from the Pacific in June 1806, they were stopped in their first attempt to cross by twelve-foot-deep snowbanks and freezing cold temperatures.31

Long term snow monitoring sites show that warming trends have greatly reduced the snowpack in the Rocky Mountains. One study found a 21 percent decline since 1915. The glaciers and deep summer snowpacks that the expedition experienced on the Lolo Trail no longer exist.32

Citations:
31 William Clark, September 16, 1805 entry, in Gary E. Moulton, Journals of the Lewis and Clark Expedition, https://lewisandclarkjournals.unl.edu/item/lc.jrn.1805-09-16; U.S. Forest Service, “Lewis and Clark on Lolo Creek,” accessed August 26, 2024, https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsm9_021246.pdf.
32 Philip W. Mote, et al., “Dramatic Declines in Snowpack in the Western US,” nature partner journals: Climate and Atmospheric Science 1 (2018): 1, 3; NPS, “Experiencing Climate,” Lewis and Clark, accessed May 21, 2024, https://www.npshistory.com/brochures/lecl/climate.pdf.

Climate Change:Lewis and Clark Trail