The ice coverage during the most recent ice age reached its maximum extent between 19,000-25,000 radiocarbon years ago, so we expect this core to cover that period and show the sequence of melting afterwards. Silt and sand values increase at the same times, probably indicating high rates of watershed erosion at the end of the ice age. Clay is the most abundant particle size during the ice age, probably formed as glacial flour.
Glacial flour is created as glacier ice grinds the underlying bedrock into very fine particles.
In the winter, when the particles are dry enough to be carried by wind, this fine material is transported for thousands of miles and is called loess. Deep deposits of loess form the bread-belt soils of North America, in Iowa, Minnesota, Illinois and Missouri. During the spring and summer melt period, the glacial flour is carried downstream and forms thick clay deposits in nearby lakes. The high clay values during the ice age indicate glaciers were present and actively eroding the Bear Lake drainage. The periodic decreases in clay amounts may represent times when glaciers were retreating or were frozen to the bedrock.