Clair River, connects Lake Huron to Lake St. Lake Huron rests in the far eastern portion of the area, known as the thumb.The Saginaw Bay forms a low basin known as the Saginaw Valley, which covers most of the region.Cass River has many branches, one of which flows into the Shiawassee River in the Shiawassee National Wildlife Refuge at 43☂2′42″N 83★9′04″W / 43.37833, -83.98444 less than a mile from where the Shiawassee merges with the Tittabawassee River to form the Saginaw River.See also List of Michigan state parks and geography of Michigan.Johnson and Son has a manufacturing facility in Bay City making Ziploc products.

The world headquarters of Nexteer Automotive is located in Saginaw. The Dow Chemical Company's world headquarters is based in Midland. General Motors operates the Flint Truck Assembly factory in Flint and Powertrain plants in Flint, Bay City, and Saginaw. The Michigan Sugar Company, which is a cooperative owned by 1,250 farmers, operates factories in Bay City, Caro, Croswell, and Sebewaing.

Several large corporations have operations in the Tri-Cities. Rural areas grow crops such as sugar beets, navy beans, corn, fruits, and fish from the Saginaw Bay and Lake Huron. Automobile manufacturing is most prevalent in Saginaw and Flint, whereas Midland is the headquarters of the Dow Chemical Company, the world's second largest chemical producer. The Flint and Tri-Cities area, as well as most of Michigan is dependent on manufacturing.

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