DID YOU KNOW

La Sal del Rey’s salt deposits have been used since prehistoric times?

By Dr. Kimberly Selber | Photos by Larry Ditto

What do Salt of the Earth, salary, and salad have in common? If you guessed salt, you’re right! But what does salary have to do with salt? Back in the day, Roman legionnaires were paid in salt – , the Latin origin of the word “salary.” Folklore tells us that sprinkling salt in a new home will ward off unwanted spirits or bad omens. And if someone has overstayed their welcome, just throw salt behind their back, and it will make them leave. Salt is an im portant commodity along with a social necessity. But did you know there is a rich salt oasis in the Rio Grande Valley?

Just south of the South Texas sand sheet lies an ancient and unique natural wonder, La Sal del Rey. This shallow salt lake, a product of millennia, forms part of the Lower Rio Grande Valley National Wildlife Refuge, attracting vis itors with its intriguing geology, history, and vibrant wildlife. This site, one of three such salt lakes in the region, is the only one open to the public, offering a fascinating glimpse into a natural process that has been ongoing for thousands of years. The lake’s origins trace back to the Pleistocene/Holocene transition, approximately 12,000 to 11,000 years ago. During this period, a drier and windier climate led to the formation of this wind-carved depression. Below it lies distinctly saline groundwater, which feeds the lake. The salinity of the lake’s water varies dramatically throughout the year, from a low of 4 parts per thousand (PPT) when nearly full to an astonishing 420 PPT as it dries, which is over ten times saltier than seawater. This seasonal cycle alternates between a deep, brimming lake and a vast, dry salt flat.

Painting by Jose Cisneros. Courtesy of the Museum of South Texas History.

As the lake dries up, a salt crust up to 20 cm thick forms, creating a stark white landscape. This salt crust is a dynamic feature, cracking and forming pressure ridges up to 0.3 meters high as it accommodates the volume expansion of the forming salt. Seeing these ridges extending for tens of meters in various directions is a marvel. Additionally, selenite (gypsum) crystals, a mere 3 cm long and surprisingly flexible, often appear on the lake’s margins.

La Sal del Rey’s salt deposits have been used since prehistoric times. Maps from the 1700s document the quarrying and trading of salt from this lake, highlighting its long-standing economic significance. The lake’s name, “The King’s Salt,” originates from Spanish colonial times when mineral resources were considered the crown’s property. During the US Civil War, the state of Texas assumed control of the salt extraction, and in 1866, a constitutional amendment privatized mineral rights in Texas, paving the way for the lake’s salt and other resources to be developed privately. Salt trade from the lake continued into the 1930s, and the brine was also used in oil and gas operations.

The question of why these salt lakes exist has been a topic of scientific curiosity. Contrary to the previously held belief that they sit atop a salt dome, extensive drilling and seismic exploration by oil companies have revealed no such structure. A more plausible explanation is the continuous concentration of brine due to the lake’s basin extending below the normal groundwater level and the region’s hot, semi-arid climate.

Today, La Sal del Rey is a popular destination for those interested in wildlife, geology, and history. The best access is from the southern entrance off Texas Route 186, followed by a 1.6 km hike to the lake’s center. Visitors can walk on the salt crust, witness the formation of salt crystals, and observe the unique ecosystem that thrives in this extreme environment. The sight of Artemia salina (brine shrimp) eggs accumulating on the lake’s margins and the seasonal transformation of the lake’s appearance offer a unique and memorable experience.

To learn more about Sal del Rey and other “Ancient Landcapes of South Texas: Hidden in Plain Sight” visit the CHAPS program at UTRGV.