Bedrock Geology

The geologic history of the area is the basis for many of its natural characteristics including topography, deposits of sand, gravel, and minerals, and its permeability.  Sand and gravel deposits may indicate the presence of substantial amounts of accessible groundwater.  However, the ability of sand and gravel to transport water quickly makes it a poor filter for pollutants from inappropriate land uses.  How close bedrock is to the surface is an important indicator of the suitability of a site for construction of buildings and septic systems.

Two kinds of bedrock predominate in Eaton.  Intrusive igneous rock is found in the northern and eastern parts of Eaton.  The youngest portion of this is Conway Granite found at Whales Back along the southeastern edge of town.  To the northwest under Rockhouse and Libby Mountains we find Two-mica Granite that is 245 to 360 million years old.   The exposed bedrock of Foss Mountain is also of this type.  Between these from Birch Hill to the northern slopes of Stewart Hill is rock formed in the Devonian period 360 to 410 million years ago.

Metamorphic rock is found in the rest of Eaton including Atkinson Mountain, the ridge from Stewart Hill to Manson Hill, Toll Hill, and Lyman Mountain.  The vast majority of this is from the Silurian period about 430 million years ago though parts of Lyman Mountain and Toll Hill are slightly younger at about 400 millions years of age.