The Deep Map

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Teaching regions

Deep cause, intact

The Black Belt

Across central Alabama and into northeastern Mississippi, a band of Cretaceous chalk (the Selma Group, roughly 75 to 85 million years old) weathered into dark, fertile soil. That soil drew cotton plantations and slavery in the 1800s, which produced today's Black-majority counties and a Democratic-voting arc that traces the old shoreline almost exactly. This is the one clean deep-cause chain on the map: rock, to soil, to settlement, to demographics, to voting.

Deep cause that reversed

Appalachian coal country

Carboniferous coal seams under West Virginia and eastern Kentucky built mining towns and a 20th-century, union-driven Democratic bloc. Since the 1970s those same counties have flipped hard Republican. The geology did not change; the politics did. Path dependence is real, but it can break.

Demographics are not destiny

The Rio Grande Valley

The south Texas border counties (Starr, Hidalgo, Cameron, Webb) are a Hispanic agricultural valley settled through irrigation farming, and they voted Democratic for roughly a century. Then they swung sharply Republican from 2020 to 2024. Starr County went Republican in 2024 for the first time in about 132 years. A group's past vote does not lock in its future one.

Demographic and political, not geological

Northern Plains reservations

Counties holding large reservations in South Dakota, North Dakota, and Montana vote strongly Democratic, but the driver is tribal sovereignty politics, not bedrock. The pattern is not uniform either: many of Oklahoma's majority-Native counties lean Republican. Read this region as demography and politics, never geology.

Read this before you read the map

Everything here is measured at the county level, averages of whole places, not individual people. Two county maps lining up does not mean any individual behaves that way; this is the ecological fallacy (Robinson, 1950). Geology never put a ballot in anyone's hand. At most it shaped soil, which shaped 19th century settlement and economics, which shaped who lives where today. Treat the deep-cause regions as historical storytelling, and treat present-day demographics as the variables actually doing the explaining: nationally the county vote is driven mostly by population density, education, and race, not by ancient rock.