In West Texas, the Sand Dunes of Monahans are a Geological Wonder

This summer your public radio station in West Texas is hitting the state parks in our area and taking a look at the stories behind the places in our backyard. First up, we head to Monahans Sandhills State Park, where the geology behind the dunes started roughly 40,000 years ago, and is part of a larger dune field that stretches across the great plains.

Out on the Sandhills of the Monahans state park, the sound of cicadas buzz as park superintendent Mike Smith climbs a roughly 20-foot dune. It’s one of the smaller hills out here.

“As I’ve said before, I’ve been blessed to be able to travel much of this country and some other as well. But this is the most difficult walking I’ve done ever in my life,” Smith laughs, as his feet crash into the soft Monahans sand.

Smith started working here in 2013, and quickly became attuned with the nearly 4,000-acre park. He lives here and even met his wife through his work at Monahans. He says there’s a certain magnetism to the park. It’s what keeps bringing visitors, like Malcolm, a regular, and one of few to have seen the entire park.

“We don’t recommend that most people try what he does,” Smith says. “It requires a lot of water, a lot of dedication, and being able to navigate with landmarks that all look the same”

But apart from the dunes, there are other landmarks here. They can serve as guides if you get turned around in the dunes. One in particular sticks out between the rolling dunes; it’s something not too uncommon in the Permian Basin: A pumpjack.

The oil-black pump is offline now. It’s fenced off and sits between some nearby picnic tables.  According to Smith, before the sandhills became a state park in 1957, some drilling activity did occur on the property, but the family who owned the land decided to do away with production.

The pump is mainly an “interpretive display now,” says Smith.

But dotted along the horizon here just outside the park’s boundary, you’ll easily spot active oil wells. In Ward County — where the Monahans State Park is — there are some 6,000 oil wells. But despite what the pump jack on the park and the thousands of wells here might suggest, the geological events that gave rise to the booming oil industry here aren’t responsible for the dunes.

Dan Moush is a research geologist with the United States Geological Survey.

“All the oil-bearing stuff is way, way older — millions of years old,” Moush explains. “So that’s way below the surface and much older.”

Piled on top of that is the pale, granular Monahans sands — the “stuff that’s in the way,” Moush jokes.

When the sands of Monahans formed it was thousands of years ago. Some trace its origins to the Rocky Mountains in New Mexico, where remnants were eroded in the Pecos River, and eventually were blown by the wind into the area. However, others like Moush say research has shown the sands could have partially derived from the Pecos River, but were more likely the result of something called the Blackwater Draw Formation, says Moush.

“[The Blackwater Draw Formation] is an unusual deposit. It’s not the kind of thing that you could easily call a sandstone or a shale, or anything like that.

“But you could think of it as a windblown sand that’s been sitting around long enough that clay has built up in it,” Moush says.

That clay throughout the millennia has been essentially wiped off and now the pale, granular sands of Monahans remains.

But no matter the geological source winds are what ultimately brought the dunes here. And to this day, they are what causes the sandy dunes to shift, sometimes up to 60 feet. So the dunes you see today might not be here in a couple months, but if you wait a while they will slowly return to their original position.

In the park, amid the seasonally shifting dunes, there are some hills pocked with vibrant vegetation: the Shinoak. The tree looks more like your run-of-the-mill desert shrub than the towering tree its name might suggest. But it plays a vital role in the rolling dunes. The tree, whose roots can reach nearly 70 feet below the surface, effectively works as an anchor.

Bob Trentham with the University of Texas of the Permian Basin says these dunes, sprinkled with Shinoak, aren’t moved by winds.

“Those are what we call stabilized dunes,” Trentham says. “They… are sand dunes, except they have now been vegetated and the root systems and the plants are holding them in place, so they don’t move.

The sands, like park superintendent Smith said earlier make for some difficult walking. But the refined surface also creates smooth conditions for the activity that draws most visitors to the park, Sand Surfing.

“I’ve seen people come out with trash can lids,” Smith said of the things people slide down the dunes with. “I’ve seen people come out with cardboard, boogie boards, surf boards.”

The best conditions for sand surfing, according to Smith, are after the area sees some rain. Rainwater dampens then compacts the sand, allowing eager duners to go faster on the way down.

 

 

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