ALAlabama Geography

Draw a line from Phenix City through Montgomery to Tuscaloosa and you have cut Alabama in half. Southwest of that line the ground is soft sediment laid down under a shallow sea. Northeast of it the rock is old, hard and folded into ridges. That line is the Fall Line, the point where rivers coming off the highlands drop onto the coastal plain and stop being navigable. Nearly every early Alabama city sits on it, because that is where the boats had to stop and where the falling water could turn a mill.

The Black Belt is a soil description first

A crescent of dark, sticky, alkaline clay arcs across central Alabama from Sumter County in the west through Dallas, Lowndes, Montgomery and Macon counties toward the Georgia line. It is roughly 25 to 30 miles wide. The clay weathers out of the Selma Chalk, a bed of compacted marine shells deposited about 80 million years ago when the Gulf reached this far inland. When Europeans arrived the belt carried prairie grass rather than pine forest, and cotton planters moved onto it for exactly that reason.

The consequences outlived the cotton. County lines, church networks, voting patterns and the route of the 1965 Selma to Montgomery march all trace the shoreline of a vanished Cretaceous sea. Alabama is one of the few places where you can read a geology map and a census map and see the same shape twice.

Two watersheds, and a river system with no rival for biodiversity

Water leaves Alabama in two directions. The Tennessee River enters the northeast corner near Bridgeport, swings west past Guntersville, Decatur and Florence, and exits into Mississippi, eventually reaching the Gulf by way of the Ohio and the Mississippi. Everything else, roughly three quarters of the state, drains south into the Mobile River basin: the Coosa and Tallapoosa joining to form the Alabama, the Black Warrior feeding the Tombigbee, all of it converging above Mobile Bay.

Where those rivers meet the sea they build the Mobile Tensaw Delta, about 260,000 acres of swamp, bayou and cypress that ranks as one of the largest river deltas in the country. The whole system carries an extraordinary load of life. Alabama has more species of freshwater fish, mussels, snails, crayfish and turtles than any other state, a consequence of having warm, ancient, never glaciated rivers that were never scraped clean. The Cahaba, running about 190 miles as the longest substantially free flowing river left in the state, blooms with Cahaba lilies in its rocky shoals every May.

Cheaha Mountain and the place where the Appalachians die

The highest ground in Alabama is Cheaha Mountain in Cleburne County at 2,413 feet, a quartzite knob in the Talladega Mountains. That is modest by national standards, and it is the point of the story: Alabama is where the Appalachian chain finally runs out. The ridges of the Valley and Ridge province narrow as they come southwest, then dive under coastal plain sediment near Tuscaloosa. The mountains are not eroded away so much as buried.

Five physiographic regions meet inside the state: the Highland Rim along the Tennessee River, the Cumberland Plateau including Sand Mountain and Lookout Mountain, the Valley and Ridge, the Piedmont around Cheaha, and the East Gulf Coastal Plain covering roughly the southern two thirds. Birmingham grew in Jones Valley because coal, limestone and Red Mountain iron ore all outcrop within a few miles of one another there. Farther northeast, the Little River runs almost its entire course on top of Lookout Mountain before cutting Little River Canyon, several hundred feet deep. Near Wetumpka, a circular ridge about five miles across marks where a meteorite struck roughly 84 million years ago.

Borders set by treaty, by river, and by clock

The eastern boundary follows the Chattahoochee River rather than a surveyed line, which is why Phenix City faces Columbus, Georgia across the water. The southern boundary runs along the 31st parallel for most of its length, then turns down the Perdido River to Perdido Bay, squeezing Alabama's ocean frontage to about 53 miles of general coastline between the Perdido and the Mississippi line. Mobile Bay and the barrier islands stretch that into hundreds of miles of tidal shoreline.

All 67 counties observe Central Time. Phenix City is the practical exception: as a suburb of an Eastern Time city, much of daily life there runs an hour ahead of the rest of Alabama.

Rain, heat, and a date that came back

Alabama averages around 58 inches of precipitation a year, putting it among the wettest states, and Mobile is routinely the wettest large city in the lower 48 at roughly 66 inches. The state record high is 112 degrees at Centreville on September 5, 1925. The record low is 27 below zero at New Market on January 30, 1966.

Hurricane Ivan came ashore at Gulf Shores on September 16, 2004. Hurricane Sally came ashore near the same beach on September 16, 2020, sixteen years to the day. Inland, Alabama sits in the part of the Southeast where tornadoes are more likely to strike after dark and to hide inside rain and forest. On April 27, 2011, dozens of tornadoes crossed the state in a single afternoon, including the one that tore through Tuscaloosa and Birmingham, and more than 250 people died.

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