Geology

To many, geology may just be a bunch of rocks. But the geology of our land influences everything from the industry of our region to where our homes are built to the ecosystems all around us. All of these things are shaped by millions of years of geological processes: the collision of continents, the formation of mountains, subsequent erosion, drastic shifts in sea level, and the thawing after the ice age.

Birmingham, more than most cities, is founded on rock. Its rapid growth stemmed from the earth below it, which held iron ore, coal, and limestone – all the key components needed to make iron and create an industrial power.

The region’s complex geology has also shaped the ecosystems of the area. As different kinds of rocks weather, they produce different soils, which support different types of plants and different animals that depend on them. For example, the limestone bedrock at Ruffner Mountain Nature Center creates calcium-rich, low-acid soils that host plants like American Basswood, Slippery Elm, and Shumard Oak, while the sandstone glades at Moss Rock Preserve are home to unusual species like Nuttall’s Rayless Goldenrod, Pineweed, and Prickly Pear Cactus. The sheer variety of rocks crammed together in our area creates many options for ecological diversity.

But where do these different rocks come from? In Birmingham, all are sedimentary rocks formed hundreds of millions ago. Rivers carried sediments to seas, and the weight of those seas compressed those sediments and altered their chemistry, with the result being new rock. Beach sand became sandstone, mud became shale, reefs became limestone, and swamp muck with its thick deposits of dead plants became coal. In fact, if you look closely, you can find the fossils of swamp plants and tiny sea creatures in rocks all around the metro area.

Then, about 300 million years ago during the Pennsylvanian geologic period, the continents that later became North America, South America, and Africa began a slow-motion collision. Over millions of years, the earth’s crust buckled, snapped, and thrust upward, thereby creating the Southern Appalachian Mountains. The last phase of mountain building ended 250 million years ago, and ever since, the mountains have been worn down by wind, rain, and gravity to become the low mountains we know today. Those two steps – first the upward thrust, then the downward wear — exposed the sedimentary rocks, which provide many of the minerals we extract through mining to support industry in the region.

Birmingham’s geology:

In much the same way that biologists have created ecoregions to help them map ecosystems, scientists who work with rock have created physiography, which divides the world into divisions, provinces, sections, districts and subdistricts depending on geology.

Parts of five physiographic provinces lie in Alabama. Two of the state’s three mountainous provinces intersect in the center of Jefferson County: the Valley and Ridge and the Appalachian Plateaus (some might know the latter as the Cumberland Plateau). Although the two provinces date back to the same series of events, they have different histories. Read more about Alabama’s physiographic sections here.

The Valley and Ridge Physiographic Province is known for its elongated ridges and intervening valleys, which run along a southwest-to-northeast orientation from central Alabama to New York. This convoluted topography developed when stress from the inter-continental collision caused the earth’s crust to deform. Throughout much of the Ridge and Valley, the continental crust was squeezed into upward and downward folds. In other areas massive sections of crust broke from the pressure and – through a process known as thrust-faulting – were pushed up and away from the collision zone. The mountains created through both processes were once steep and tall, but millions of years of erosion have worn them down to narrow ridges of durable rock that are the area’s mountains. Sandstone, which is exceptionally strong, is usually the rock found on the tops of the region’s mountains. It protects softer rocks beneath from erosion. The adjacent valleys are where the sandstone was fractured by mountain-building processes. The broken sandstone and much of the softer rocks beneath have eroded away.

Here in Birmingham, the most famous ridge is Red Mountain, a long linear ridge stretching many miles through north central Alabama. The corresponding valley, Jones Valley, contains most of Birmingham. The pattern is echoed in other ridges across the region: Shades Mountain, Oak Mountain, Double Oak Mountain, plus several smaller ridges crossing the metro area. Red Mountain is different from these other mountains in several ways. Most notably, it contains layers of hematite, or iron ore, and it lacks a layer of sandstone at its very top.

The Appalachian Plateaus Physiographic Province is found in the northern tier of the Birmingham metro area. In the portion of it found here, the Cumberland Plateau Section, areas of the up-thrusted crust have eroded in a different way, creating a network of broad, level mountains (e.g., Sand Mountain) with hard sandstone on top and softer sediments like limestone in the valleys below. Around Birmingham, the sandstone cap was thinner and most of it has eroded away. The softer sediments beneath are now eroding quickly in terms of geologic time. This has created the shale hills of northern Birmingham and beyond. Below those hills lie rich coal beds that are mined in the Warrior Basin.

 

Geology of Homewood Forest Preserve

A hike through the preserve can take you across three different geologic layers that span more than 325 million years of earth’s history. The lower section of the preserve along the creek is made up of recently eroded material deposited … Continue reading

Geology of George Ward Park

The city of Birmingham contains a unique geological occurrence in which a variety of rocks and minerals needed for iron and steel production are found with a small geographical location. The city flouished due to close proximity of iron, limestone, … Continue reading

1930’s Stone Work in Parks

A City of Birmingham bond issue in 1931 provided $500,000 in funds for the Parks Board to hire unemployed workers to build recreational structures in Birmingham city parks. In Green Springs Park (now George Ward Park), they re-graded and sodded … Continue reading

Geology Cahaba River Walk

The topography of the Cahaba River Walk consists of small rolling hills typical of the Birmingham area.  The Alabama Ridge and Valley created these curls of land when the African Plate collided with the North American Plate in the Paleozoic … Continue reading

Geology of Avondale Park

Adventurous visitors to the park early last century would explore the cavern ,,, Continue reading

Geology Map Red Mountain Cut

Virtual Tour of Red Mountain Cut Signs

When the trail along Red Mountain Cut was first opened the Red Mountain Museum set out signs to explain the features of this amazing natural wonder. Over the years the signs have had their share of weather and human impacts. … Continue reading

Geology of Red Mountain Cut

Before the ‘Cut’ was created to build an expressway linking downtown Birmingham and the neighborhoods south of Red Mountain, the mountain’s geological features remained hidden in the rock but slicing through the mountain changed this drastically. Now, 190 millions of … Continue reading

Geology of AWC

Oak Mountain State Park sprawls across the ridge of Double Oak Mountain, actually twin ridgelines, an unusual feature that probably inspired the mountain’s name. Between the two ridges is a shallow valley and a small stream, Peavine Branch, that begins … Continue reading

Lost Worlds of Alabama at Moss Rock Preserve

Sandstone canyon between boulders

We are so glad you asked!  Here is a question about Moss Rock Preserve answered by Jim Lacefield – follow the page references in Lost Worlds in Alabama Rocks: A Guide to the State’s Ancient Life and Landscapes (2nd Edition) … Continue reading

Geology of Railroad Park

Railroad Reservation, designed as the hub of freight travel in the 1880s, sits in the Jones Valley on the lowest part of the Conasauga Formation, an extensive thin slab of limestone. Jones Valley rests below what was originally one of … Continue reading

Geology under the springs

The Watercress Darter National Wildlife refuge sits in Jones Valley, the long, low-elevation area to the north of Red Mountain. The valley’s bedrock was formed back in the Cambrian Period (542–488 million years ago). Most of this rock is limestone … Continue reading

Geology of Roebuck Spring

Geologically speaking, Jones Valley is a dynamic place to live. Due to its karst topography, sinkholes threaten to open at any moment, springs burst from the ground, and there are underground caverns beneath our feet. Several rock formations form the … Continue reading

Geology of Shades Creek Greenway

Frog stranglers, gully washers, turtle floaters. Whatever you call an intense downpour, Birmingham gets a lot of them. When it rains that heavily, most of that stormwater flows downhill to our creeks. As the creeks rise, they spill over into … Continue reading

Jones Valley: Where did it come from?

Ever heard of Jones Valley? If you visit, live, or work in downtown Birmingham, you’ve spent time on the floor of this valley. Jones Valley is the long valley lying along the northern side of Red Mountain. It was an … Continue reading

Geology of East Lake Park

East Lake lies within the Jones Valley, a relatively level terrain to the north of Red Mountain. The park rests above a series of rocks known as the Conasauga Formation, a set of rock layers that include limestone, dolostone, and shale. … Continue reading

Hematite: a Rock Made by Bacteria and Ocean Waves

Sample from Red Mountain Formation

The ore that made Red Mountain famous can be found along the trails at Red Mountain Park. The rock is called hematite, or iron ore, and it’s unusual in many ways. To begin with, it’s far richer in iron than … Continue reading

Gaps in Our Knowledge of Geologic History

There’s a new way of thinking about the geologic history of the Southern Appalachian Mountains. Read most summaries about their origins and you’ll learn the Appalachians arose during the last third of the Paleozoic Era. The authors will likely explain … Continue reading

Red Mountain Park Geology

Red Mountain is composed of several distinct rock formations. All have been uplifted and tilt up and toward the northwest. The Chickamauga Limestone is the oldest of these formations and makes up most of the northwestern face of the mountain.  … Continue reading

Geology under McWane Science Center

Like much of downtown Birmingham, the McWane Science Center rests on a foundation of rock known as the Conasauga Formation. This formation is found in Alabama, Georgia, and Tennessee and includes layers of limestone, dolostone, and shale. These rocks are … Continue reading

Geology of Turkey Creek

This small Nature Preserve holds the most complex story of geology found in all of the Trek Birmingham sites. To truly understand what happened, come visit, walk the trails, and touch the fossils imbedded in the canyon walls. The first … Continue reading

Geology of Birmingham Botanical Gardens

The hilly, northern portions of The Gardens are underlain by the Hartselle Sandstone.  The layer is formed of sand and other offshore sediments deposited when the region was a shallow sea in the Mississippian Period (318-359 million years ago). This … Continue reading

Geology of the Birmingham Zoo

Though you won’t see this rock at the surface, the Birmingham Zoo is underlain by a formation known as the Floyd Shale and Bangor Limestone Undifferentiated. This layer is predominantly shale with an intermingling of limestone and some mudstone. These … Continue reading

The Rocks of Ruffner

There may not be gold in them thar hills, but if you know where to look, it’s easy to find colorful and ancient rocks while walking the trails at Ruffner Mountain Nature Preserve. Think of the mountain as a layer … Continue reading

Geology of SEC and Hugh Kaul Ecoscape

The SEC and the Hugh Kaul Ecoscape are on the Birmingham-Southern Campus.  The college – known to many as The Hilltop –  is on one of the many hills of dolomite and chert found on the floor of Jones Valley. … Continue reading

Geology of Sloss and the making of “The Magic City”

Today, Sloss seems a bit like a fish out of water, old blast furnaces sitting in a modern downtown. The location of the furnaces is due to geologic processes that began 300 million years ago and involved ancient oceans, swamp forests … Continue reading

Geology of Moss Rock

Moss Rock Preserve is within the Cahaba Ridges District of the Tennessee Section of the Valley and Ridge Province. The Preserve is bisected by Hurricane Branch which flows northeast through preserve.  This small creek divides two big mountains. To the … Continue reading

Geology of Vulcan Park

Birmingham grew on a diet of rock. The city’s growth was fueled especially by the iron ore mined from Red Mountain, the long ridge Vulcan perches atop. The story of the mountain’s geology is the story of Birmingham’s deep history … Continue reading

Moss Rock: The Boulders

On any given weekend you’ll find an unusual addition to Moss Rock’s native ecology: boulderers. The preserve’s enormous stones – some of them the size of houses – were known to climbers long before it became a public park, and … Continue reading

Geology of Oak Mountain State Park

Oak Mountain State Park sprawls across the ridge of Double Oak Mountain, actually twin ridgelines, an unusual feature that probably inspired the mountain’s name. Between the two ridges is a shallow valley and a small stream, Peavine Branch, that begins … Continue reading

What Lies Beneath: Karst

It took millions of years to create the special geology that is now Birmingham – and now it’s slowly dissolving away. Jones Valley is part of a sub-region characterized by valleys with limestone and dolomite bedrock, and the thick layers … Continue reading

Geology of Ruffner

Red Mountain forms the backbone of the Ruffner Mountain Nature Preserve. The mountain and its adjacent valleys lie within a portion of the Valley and Ridge physiographic province. This province extends from central Alabama to New York and is known … Continue reading