Field Guide: the Smackover Formation

An ancient, hidden coastline is about to fuel an Arkansas mining boom

Apologies for my absence over the past few weeks. I was wrapping up edits on my book (!) and then traveling for my honeymoon in Alaska. I’m finally getting caught up and should be back to regularly scheduled newsletters next week.

An oil rig in El Dorado, Arkansas, in the 1920s. Arkansas State Parks.

The geology of the South can be subtle. Our mountains are old and weathered. There are places—like the southern edge of Arkansas—where for hundreds of miles the land is so flat and unchanging that you can forget it’s geological at all.

But there’s always a story in the terrain—or underneath it.

For millions of years, the Gulf of Mexico reached far northward, covering much of what is known today as the coastal plain. That means beneath today’s soils lies an ancient seabed—mud that has since hardened into, among other materials, a limestone aquifer.

The “Smackover F…