The big spring flows from a small aquifer deep within the soils. Imagine a tilted bowl with a chip in the upper edge. As that bowl fills, the water is contained until it reaches the chip, then the water spills out. The spring site is very similar. The aquifer it flows from is relatively small, with it's sides formed roughly by the surrounding hills. The interior is filled with porous limestone and sands from the Cretaceous period which existed from 79 million to 145 million years ago. For millions of years, rainfall and groundwater would fill this bowl, or aquifer, and the spring would flow freely to the surface. When man arrived and began drilling water wells and pumping water out of the aquifer, nature could not replace it fast enough and the spring ceased to flow. In 1880, a survey conducted by the Texas and Pacific Railroad estimated that approximately 100,000 gallons of water per day were flowing from the spring. Today, during years with above average rainfall, the spring still flows but at a much smaller rate.
Long before man arrived, the tall grasses of the Southern Great Plains supported huge numbers of mammals, many of which are now extinct. The spring and surrounding grasslands supported the giant armadillo, the four-horned antelope, giant anteaters, immense ground sloths, the ancient horse, and miniature camels.The bones of mastodon and mammoth have been found near the spring. These giant relatives of the modern day elephant needed large amounts of water to rehydrate, and rarely strayed too far from dependable water sources. Great predators such as dire wolves and saber-tooth tigers preyed on the herd animals, and their remains have have been found nearby.
The greatest predator of all - humans - probably first appeared around the spring area as tribal bands of hunter gatherers between 12,000 and 16,000 years ago. They followed the great herds just like the wolves and saber-tooth tigers. Many of the mammals at the time used a stationary herd defense to protect their young.This meant that instead of running, they would stand to intimidate potential predators. This did not work with the intelligent humans and their dart hurling atlatl. The atlatl, or spear-thrower, is an ancient tool that cleverly utilized a carved short stick to dramatically increase the velocity, power, and range of a specialized spear or dart. The atlatl allowed ancient hunters to pursue the largest and most dangerous game on the prairies, including the mastodon and the giant ancient bison. Gradually, climate change and human predation caused the extinction of many of these magnificent mammals. In their place, huge herds of American bison and pronghorn antelope developed on the fertile prairie surrounding the spring.
The prairie had a symbiotic relationship with many of the animals that inhabited it. The herds of buffalo eliminated the encroachment of trees. Prairie dogs, whose villages sometimes covered hundreds of square miles, ate the tender roots of trees including the mesquite. Massive prairie fires that sometimes burned for months at a time scorched the Southern Great Plains. The grasses that inhabited the area developed very deep roots to allow for the revegatation of areas burned by fires or grazed by the buffalo. Only in the deeper arroyos did tree species such as mesquite and juniper escape the buffalo herds, prairie dogs, and grass fires. With the introduction of the Europeans, cattle and sheep became established in the region. Many of the taller grasses of the prairies were not genetically adapted for these new species, and they gradually disappeared as more and more cattle and sheep were confined to fenced pastures . Settlers attempted to limit the burn areas of the prairie fires. They also all but eliminated the prairie dog villages because their livestock sometimes stepped into a prairie dog burrow and broke an ankle. Buffalo were eliminated in order to control the Comanche. Mesquite and juniper moved out of the arroyos and into open range land, their shadows not allowing native grasses to flourish. In less than 10 years, the flora of the Southern Great Plains forever changed.