The Thumb region of the Lower Peninsula of Michigan is a post-glacial landscape where northern forest blends with central hardwoods, bordered by Lake Huron, the Saginaw Bay, the Saint Clair River, and Lake Saint Clair. There are differing opinions about exactly what geographic areas are included in the Thumb, which is named because the Lower Peninsula is shaped generally like a large mitten, and the Thumb like the thumb of the mitten. Historically, most people have probably considered the Thumb to be limited to that area from Port Huron north, and from the Saginaw Bay east. The Thumbland Conservancy has taken a slightly broader view of what constitutes the Thumb.

We basically drew a straight  line from the south end of Saginaw Bay and extended it to the northwest end of Lake Saint Clair. By this definition, the Thumb includes at least part of Macomb County in addition to the more traditional Thumb region of Saint Clair, Sanilac, Huron, Tuscola, and Lapeer Counties. Considering watershed boundaries, the Thumb could be expanded even further to include parts of Bay, Saginaw, Shiawassee, Genesee, and Oakland Counties. But sticking to the idea that the region is a big thumb, the TLC definition is fairly close to an anatomical thumb, although there is some debate about how much to include as the lower knuckle or metacarpophalangeal joint. We are pretty sure that when Paul Bunyan put his hand in the mud in lower Michigan, he didn’t mean for it to be too complicated.

The Thumb is a great place with so much worth protecting. For those who know the Thumb, there really seems to be no end to the fascinating natural areas, historical sites, points of interest, and cultural history. The Thumb is actually quite unique on a global basis. Few regions border as much fresh water as the Thumb, nearly surrounded by the Great Lakes, including Lake Huron, Saginaw Bay, the Saint Clair River, and Lake Saint Clair. The south end of the Thumb, where the Saint Clair River flows into Lake Saint Clair, is one of the largest freshwater deltas in the world, including Harsens Island, Dickinson Island, and Walpole Island in Ontario. The Thumb is crossed by many rivers including the Black River, Mill Creek, Cass River, Flint River, Clinton River, Pine River, Belle River, Salt River, Sebewaing River, Pigeon River, Pinnebog River, New River, and Willow Creek, along with the many tributaries. The Black, Belle, and Clinton Rivers are known particularly for their diverse and resilient fish and mussel communities, with many rare species.

The Thumb is a post-glacial landscape of rolling glacial till plains where the last glacier churned out vast piles of sediment; a flat perimeter of lakeplain along the current Great Lakes where an expanse of glacial meltwater once covered the land as much as 40 miles inland; a higher interlobate region formed between the Huron and Saginaw ice sheet lobes, of large hills and scattered pothole lakes formed by huge chunks of ice left behind by the last melting glacier; the Port Huron Moraine, a broad ridge paralleling the lakeplain marking the edge of the last melting glacier as it stalled during a colder climate period; eskers or ridges of sediment that were deposited in huge drainage channels under the glacier, such as Deanville Mountain; and other unique features formed or revealed by the interaction of the glacial melt waters and present-day Great Lakes with the shoreline area such as the dune and swale complex, Rush Lake, Lake Huron bluffs and ravines, sandstone outcrops, beaches, dunes, and Sand Point. The variety of landscapes across the Thumb has resulted in at least as many unique natural communities including Great Lakes marsh, dune and swale complex forest, lakeplain prairie, lakeplain oak openings, southern hardwood swamp forest, hardwood conifer swamp forest, mesic flatwoods, bog, fen, mesic and dry-mesic southern upland forests, mesic and dry-mesic northern upland forests, floodplain forest. Some of the Thumb’s largest and most impressive examples of these natural communities are the Great Lakes marshes along Saginaw Bay and the Saint Clair River Delta, the dune and swale complex of Port Crescent, lakeplain prairie along Saginaw Bay, the large expanses of forest in the Verona, Deford, Tuscola, Vassar, Lapeer Deford, and Port Huron State Game Areas, the nearly 8-square-mile Minden Bog, one of the southern-most raised bogs in North America, and the Minden City State Game Area, the high interlobate hills and lakes region extending from the Kingston area southwest through Lapeer County, and the vast stretch of mesic northern forest and other forest types and associated species of the Port Huron State Game Area and other large forests.

Over 200 rare species have been documented across the six counties of the Thumb region. Some of the more iconic species include Lake Sturgeon, Eastern Sand Darter, Northern Riffleshell mussel, Rayed Bean mussel, Eastern Fox Snake, King Rail, Cerulean Warbler, Prairie White-fringed Orchid, and Painted Trillium. Thanks to the foresight of federal and State leaders, decades ago, over 160 square miles of State recreation land in 29 State Game and Wildlife Areas were established across the Thumb, including the St. Clair Flats SWA, St. John’s Marsh SWA, Deford SGA, Tuscola SGA, Lapeer SGA, Minden City SGA, Verona SGA, Port Huron SGA, Fish Point SWA, Wildfowl Bay SWA, Quanicassee SWA, Vassar SGA, Murphy Lake SGA, Rush Lake SGA, Sandusky SGA, Sanilac SGA, Gagetown SGA, and Cass City SGA. There are also over 8 square miles of State recreation land in 6 State Park and Recreation Areas including Port Crescent SP, Sleeper SP, Lakeport SP, Algonac SP, Wetzel SRA, Metamora-Hadley SRA, and Sanilac Petroglyphs HSP. Numerous county parks, township parks, a few nature centers, several nature preserves, camps, public access sites, and trails are scattered across the Thumb also.