Geologist outlines how Pine County’s ancient bedrock and glacial history shape Snake River behavior and land‑use risks

A geologist who mapped Pine County’s bedrock and glacial deposits told the county board that ancient bedrock, repeated glaciations and large subglacial drainage events fundamentally control the Snake River’s course, gradients and erosion behavior — findings that matter for shoreline development, trail planning and water‑quality work. Carrie Jennings, who prepared a county geologic atlas years earlier and conducted a Snake River presentation, explained how ~1.1 billion‑year‑old basalt flows, uplifted sandstones and much younger glacial deposits create a landscape where the river alternates between low‑gradient lake reaches and steep, rock‑controlled rapids and nick points. Jennings described how the river is still adjusting to dramatic drainage events tied to Glacial Lake Duluth and other ice‑marginal lakes. She pointed out that some reaches have low gradients with adjacent wetlands and lake‑like conditions, while others encounter sandstone or basalt outcrops that form steps and rapids. Why it matters Jennings told the board that geology determines where shallow floodplain areas and steep eroding bluffs form, and that vegetation and setbacks reduce bluff failures and erosion. She recommended local tools that other counties use — such as steep‑slope or bluff setbacks and vegetation standards — to reduce risk to structures placed too close to actively migrating river meanders. She also highlighted areas where lake or wetland deposits are likely to affect groundwater movement and water quality. Local implications and public comment Board members asked about aquifer vulnerability, and Jennings said Mount Simon / related sandstone units are thin in Pine County and susceptibility maps in the county geologic atlas show areas more vulnerable to contamination. A public comment at the meeting noted the river is a recreational asset and emphasized that land‑use and maintenance funding are long‑term considerations. Ending: The presenter said the geologic perspective should inform watershed planning, trail and bridge siting and local setback policies; commissioners thanked her for the briefing and asked staff to consider how to incorporate geology into project planning.