Topography Tells the Tale

Everyone knows the Great Plains are flat, and the High Plains/ Llano Estacado are so flat that they make pancakes look like the Appalachians and Alleghenies. You can stand on a tuna can in Dalhart, TX and see all the way to Wichita, KS. Except . . . once you start walking the ground, you discover that it ain’t necessarily so. Especially if you are walking in spring, during or just after the rainy season.

The entire High Plains* slopes from northwest to southeast, the interruption of the Canadian Breaks and Palo Duro Canyon complex notwithstanding. At its highest, the elevation is almost 6000′ above sea level, down to about 1500′ ASL at the southern tip of the Llano Estacado. Within that range, however the surface does appear relatively flat. OK, bowling lane flat for people who are used to having a little roll to their terrain. There’s nothing to give a sense of distance or scale, unless you count knee-high grasses. However, once you start becoming familiar with the region, the differences appear. They are not as marked as, oh, the Flint Hills of Kansas, or the Sandhills of Nebraska, or the Front Range and Sangre de Christo Mts. In fact, you need to look down and out rather than up in order to see the difference.

Prior to the advance of the plow, and even after, shallow depressions called playa lakes covered the High Plains (pronounced “ply-uh”). Even today some 25,000 – 30,000 “official” playas dot the region. The origin of these thousands of depressions remains a matter of some controversy, with ideas ranging from the possible to the eye-wateringly wild. Many people traditionally attributed them to buffalo wallowing in the dust, making deeper and deeper dust-baths over the course of centuries. However, what made the dusty areas for the buffalo in the first place? Other suggestions include proto-sinkholes, caused by groundwater dissolving the layers of salt and gypsum under the surface. In some areas, and some cases, this is probably valid, notably the east-central and eastern High Plains, where sinkholes are an ongoing concern.

Meteorite impact craters have been nominated, and one theorist argues that the playas and similar structures in the Carolinas and other parts of the US are evidence of a massive extinction event that occurred 12,000 years ago that caused the end of the Pleistocene megafauna (Mastodons and the Meteors of Doom [with apologies to Luis Alvarez]). Wind, aka aeolian erosion, combined with one of the above is also possible, and most students of playa formation now agree on a combination of the above theories, with different playas forming different ways. However they formed, playas became vital components of the recharge system of the Ogallala Aquifer in the High Plains and provide water, forage, and shelter for all sorts of critters from spring to autumn. They also act as flood prevention catchments (until people build houses in them), holding up to 90% of the runoff from the surrounding uplands.

A nice playa with gradations in the plants around it. From HPPR.org.

A nice playa with gradations in the plants around it. From HPPR.org.

The cracked clay bottoms of most playas allows water to percolate relatively rapidly. This sends moisture down into the groundwater and out into the soil, making playas oases for plants and animals. It also channels water that might have evaporated into the soil.

If you walk toward the center of a playa, you start in the short-grass.  Farther down the slope, the grasses grow longer, and western wheat grass and vine mesquite (a grass in the Panicum family) appears along with other mid-grasses, amaranth (pigweed) and curly dock and water dock. This is the moister ring, where groundwater lingers. When you pass out of the taller grasses and wildflowers and forbs, don’t be surprised if the ground goes “squish” under your boots. Sedges and reeds appear and you may very well find open water ahead of you, with more cattails, arrowhead, and bulrushes. Brine shrimp and bugs (like mosquito larvae) dart around the water, while ducks and geese paddle and killdeer stalk the playa edge. Open water means that you may well be looking at a spring-fed playa, or one of the deep rainwater playas. Or it is a wet year. Or yes. Buffalo Lake in north-central Amarillo (now in MLK Junior Park) was a spring fed playa, now rain dependent.

Don’t drink the water. Cows, horses, pronghorn, ducks, cranes, and everything else drinks from the shimmering water, and leave bacteria behind. Some playas, especially south of Palo Duro canyon, in the Brazos River drainage, are salt lakes. You really don’t want to drink from those, unless you know the few where freshwater springs bubble up at one edge.

Playas are considered an endangered landform because people keep plowing them up or filling them in. I was especially peeved to see a spring-fed playa south of Amarillo filled in and turned into more tract housing. Red-wing blackbirds had hung out there, as had ducks and geese. I’d hoped someone would buy it and turn it into a park, or that the developer would not get the necessary permits, but it happened, and another playa is no more than a memory. WInd-turbine farms interrupt playas and the drainages that support them.  Farmers dig drainage pits into other playas to use recycling irrigation water (back when flood-furrow was the only way to go).

That said, in the past 15 years, more people have come to appreciate playas and work to protect them. The Playa Lakes Joint Venture is one group, as is Ducks Unlimited. Individual landowners also protect playas from disruption and invasive species. The future of the playa lakes looks better than it has.

*High Plains, as is customary in this blog, refers to the shortgrass steppe south of the Arkansas River, east of the Pecos.

 

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