page_title: Hunterdon County, New Jersey
section_title: Geology
hierarchical_section_title: Hunterdon County, New Jersey / Geology
caption_attribution_description: English: A bridge in the Califon, NJ Historic District. This is an image of a place or building that is listed on the National Register of Historic Places in the United States of America. Its reference number is 76001157
context_page_description: Hunterdon County is a county located in the western section of the U.S. state of New Jersey. As of the 2019 Census estimate, the county's population was 124,371, making it the state's 18th-most populous county, representing a 3.1% decrease from the 128,349 enumerated in the 2010 United States Census, in turn increasing by 6,360 from the 121,989 counted in the 2000 Census. Its county seat is Flemington.
  In 2015, the county had a per capita personal income of $80,759, the third-highest in New Jersey and ranked 33rd of 3,113 counties in the United States. The Bureau of Economic Analysis ranked the county as having the 19th-highest per capita income of all 3,113 counties in the United States as of 2009. Hunterdon County is noted for having the second-lowest level of child poverty of any county in the United States.
  Geographically, much of the county lies in the Delaware Valley as a geographic concept, that is, the drainage basin of the Delaware River. Local businesses and the Delaware Valley Regional High School carry the name.
context_section_description: Around 500 million years ago, a chain of volcanic islands shaped like an arch collided with proto North America and rode over the top of the North American plate. The rock from the islands created the highlands of Hunterdon County as there was a shallow sea where Hunterdon County is now located.  Then around four hundred million B.C., a small continent that was long and thin, collided with proto North America. This collision created compression, which caused heat. The Paleozoic sediment of shale and sandstone folded and faulted. The heat allowed the igneous rock to bend, thus Hunterdon County was born.
  The African plate which later collided with North America created more folding and faulting, especially in the southern Appalachians.  Then the African and North America plates tore and drifted away from each other.
  The Wisconsin glacier that entered into New Jersey around 21,000 BCE and then melted around 13,000 BCE did not reach Hunterdon County. However, there are glacial outwash deposits from streams and rivers that flowed from the glacier southward depositing rock and sediment.
  Hunterdon County has two geophysical provinces.  The first is the Highlands which is the western section of the county.  The other is the Piedmont which is the eastern and southern section of the county.  The Highlands account for one-third of the area and Piedmont accounts for two-thirds of the county.
  The Highlands are part of the Reading Prong.  Limestone and shale over igneous rock comprise the Highlands.
  Piedmont includes the Hunterdon Plateau and the Raritan Valley Lowlands which are 150 to 300 feet (46 to 91 m) above sea level.  Piedmont is made up of shale and sandstone.
caption: The bridge over the South Branch of the Raritan River in Califon.
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