Traveling across the prairie is always an adventure, but there is one thing that can stop any prairie traveler in their tracks: gumbo.

What is gumbo? The easy answer is that it’s just mud, but it’s not your average mud.
You might think to yourself, “How bad can mud be?” Anyone who has experienced gumbo firsthand will likely respond: “It can be pretty bad.”

The scientific explanation of gumbo is a bit more dense. Gumbo’s more technical name is bentonite clay or aluminum phyllosilicate, which primarily consists of the mineral montomorilonite. According to the U.S. Geological Survey, bentonite formed from deposits of volcanic ash that settled to the bottom of vast sea beds between the Tertiary to Mesozoic periods (up to 230 million years ago). The word bentonite comes from the Benton Shale, which was the first bentonite deposit ever discovered. It was named after Fort Benton, Montana by W C Knight in 1898 and extends across Montana, Wyoming, North Dakota, South Dakota, Colorado, Kansas, and Nebraska.

Gumbo happens when water comes into contact with bentonite; it attaches to the bentonite crystals through an electrochemical reaction, causing bentonite to expand up to 14 times its dry mass. It also brings out the soil’s adhesive properties.

This is when things get sticky and, if you’re traveling in a remote part of the prairie, potentially hazardous.

Gumbo sticks to virtually anything it touches, turning even a simple walk or drive across the prairie into a difficult, muddy mess. It’s also incredibly slick, especially when on a hill, as demonstrated by our Reserve staff in this video.

When vehicles drive through gumbo, it creates deep ruts. When the mud dries, it sets like concrete and is about as heavy. The frozen ruts remain very hard and should be navigated carefully. If muddy conditions are followed by cold weather, the ruts will freeze and become difficult to navigate. And when the snow and ice thaws, the gumbo starts all over again until it dries or re-freezes.

Many roads on the prairie become completely impassible when wet, even in a four-wheel drive vehicle. Much of the travel to and across the prairie takes place on gravel or unimproved dirt roads, so travel across these roads requires preparation and planning. Always watch the weather before embarking on a trip, and if rain or snow is in the forecast, leave extra time for travel or consider postponing your trip. Local tow services will only retrieve stuck vehicles when conditions have improved.

American Prairie Reserve Safety Manager Dan Stevenson has a fairly straightforward recommendation for dealing with gumbo: “Don’t be there when it occurs.”

“Advance trip planning and reviewing weather forecasts are extremely important when it comes to not getting caught in severe gumbo,” Stevenson explains.

Our Road and Weather Conditions page contains up-to-date information on the status of roads across the prairie, but before a trip always monitor the weather forecast for the areas you plan to travel.

Gumbo has been bogging down prairie travelers as long as humans have lived in and explored this area, long before extended forecasts were at our fingertips. On the Lewis and Clark Expedition, William Clark wrote “the bank and the bluff they are obliged to pass are So Slippery and the mud So tenatious that they are unable to bare their mockersons.” Meriwether Lewis also expressed his vexation with the mud: “I attempted to walk on Shore Soon found it verrry laborious as the the mud Stuck to my mockersons and was verry Slippery.”

Travel on the prairie is still often dictated by nature’s terms, not ours. While gumbo is certainly a force to be reckoned with and warrants our caution, it’s also an example of what makes this place so wild and special.