The Sangamon Stage is a geological term used to designate one of the intervals between the successive advances of glacial ice across the landscape of North America. Also known as the Sangamon Interglacial, the period is so named because the distinctive soil that formed during this period was originally described from samples taken from water wells in northwestern Sangamon County.
This Sangamon Soil, a greenish-gray, poorly- drained soil type that formed when plants and weather altered the silts left behind by the melting Illinoian-era glaciers, is widespread across the continent.
The Sangamon Stage began about 125,000 years ago, when the climate gradually warmed, creating conditions not very different from today’s. This interval of moderate weather lasted until the gradual return of the ice sheets. This most recent of the incursions of glacial ice into Illinois, known as the Wisconsin Stage, began approximately 75,000 years ago and lasted until about 10,000 years ago.
A display at the Illinois State Museum depicts a summer day in Montgomery County as scientists imagine it to have been during the Sangamon Stage.
Contributor: James Krohe Jr. 
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