Geologist outlines Snake River's geologic controls and implications for trails, erosion and development

Carrie Jennings (Speaker 11), a geologist who previously prepared a Pine County geologic atlas, gave commissioners a technical briefing linking bedrock geology, glacial deposits and modern river behavior. Jennings described billion‑year‑old basalt and sandstone units, glacial sublobe deposits and subglacial drainages that control sediment distribution, and she explained how these factors translate into reaches prone to erosion, bluff formation and differing flood responses.

Jennings emphasized the practical implications for public infrastructure and land use decisions, noting that some reaches are low‑gradient and prone to sediment delivery and others are actively incising and forming bluffs. She encouraged setbacks and vegetation maintenance to reduce slope failure risk and discussed examples where engineered riprap provided only short‑term protection. "So, really, the best strategy for reducing risk of slope failure and loss of property is to avoid placing structures too close and to maintain vegetation to stabilize the slopes," Jennings said.

County commissioners said the geologic perspective was useful for future trail planning and for thinking about setbacks, floodplain management and where to avoid infrastructure. The presentation will be incorporated into watershed and trail planning conversations.