 The moraines and outwash plains contain sand and gravel deposits that are more permeable than the fine-grained glacial till and lake clays found in the downstream.The upper half of the watershed has variable (high) relief and is generally well-drained with numerous shallow aquifers that contribute groundwater flow to the headwaters of the Shiawassee River.The Lower Shiawassee is bordered by a low-relief till plain overlain by relatively impermeable and are poorly-drained fine-grained glacial lake clays and relict beach deposits that were deposited over a several thousand-year period when glacial Lake Saginaw covered much of the area, after the most recent retreat of the ice at the end of the Wisconsin glaciation.