That’s a monumental challenge in a state where 96 percent of land is privately owned. There are basically two ways to preserve privately owned land as open space: buy it outright, or ask a landowner to donate or sell his or her development rights through a conservation easement, a legal agreement that permanently restricts land use. The Great Springs Project is using both strategies. “Every landowner with whom we’ve spoken, they already have a stack of letters from people saying, ‘Do you want to sell your property?’ ” Merritt says. He scours real estate listings every day, looking for parcels to acquire. “We’re out there paying market prices. No one is giving us a discount.”

This is expensive work. A few weeks before our hike, the nonprofit had put under contract an 844-acre ranch just north of the trailhead that was listed for more than $8 million. In this instance, the Great Springs Project doesn’t own the land—it facilitated the deal with conservation-minded buyers—but the organization still must have ample cash on hand for transactions. So how much will the Great Springs Project cost? Merritt hedges, unwilling to commit to a budget. It depends on the proposed trail alignment, how much public funding becomes available for parks, and how willing landowners are to donate land or sign conservation easements. The ultimate cost, he allows, is likely to be hundreds of millions of dollars. The goal is to complete both the trail and conservation work by 2036, the Texas bicentennial. Three years in, the nonprofit has conserved roughly five thousand acres, 10 percent of its goal. 

Back on the trail in San Marcos, Skrobanek stops suddenly in front of an amphitheater-shaped hole in the ground. Layers of limestone and brush give way to an opening in the earth so tidy, it looks man-made. Had it rained today, we could have watched as water filtered through the brush and poured into this recession, known as a karst feature, named for the landscape formed from the erosion of limestone and other soluble rocks. If the aquifer is a bathtub, recharge features like this one are the faucets.

“This is fundamental to why we’re doing the work that we are,” Merritt says. These features, which can be as small as a fist or as big as a pickup, are concentrated in the twenty-mile-wide band of the aquifer’s recharge zone. Paving over this area means covering the thousands of faucets that supply the aquifer. New construction also strips the land of its natural filtration system of foliage and topsoil, threatening both water quality and quantity. And more development means that less water can enter the aquifer during heavy rains, increasing the risk of flooding for everyone living on this vast, fragile system.

Most of Texas operates under a legal doctrine called the rule of capture, which basically means if you can pump it, you can keep it—landowners own the rights to the groundwater below their land. One exception is in the eight thousand square miles of land under the jurisdiction of the Edwards Aquifer Authority, the agency tasked with keeping the Comal and San Marcos springs flowing. After it began operations in 1996, the EAA focused on regulating water coming out of the aquifer by issuing permits and making sure wells were being maintained. Over the past couple of years, the agency has shifted its focus to input. The EAA now uses a similar approach to that of the Great Springs Project, working directly with landowners to buy property outright or put conservation easements in place. On the EAA’s 151-acre research park outside of San Antonio, geologists study the best land management practices to maximize recharge on the land the agency controls. One of these is relatively simple and cheap: building berms and swales, which are low retention walls and broad, shallow bowls designed to slow water down as it rushes downhill, increasing infiltration into the aquifer.

After our hike, I head three miles northeast to San Marcos Springs, one of the most prolific outflows of the Edwards Aquifer. Here at Spring Lake, hundreds of small fissures release more than 100 million gallons of water every day, which pools into the lake before flowing south as the San Marcos River. Indigenous people in Central Texas have long performed religious ceremonies at these springs, where archaeologists have documented evidence of human habitation going back at least 11,500 years, making this one of the oldest continually inhabited sites in North America.

The springs were—and are—considered sacred, says Mario Garza, an elder of the Miakan-Garza Band and the founder of the Indigenous Cultures Institute, based in San Marcos. “When we lost the land, we lost all our sacred sites that were on the land,” Garza says. Today, if tribal members want to access the springs to perform religious ceremonies, they have to abide by the same rules as everyone else—be out by nightfall, no fires or smoke or loud noise (which precludes singing and drumming). His colleague Maria Rocha, also a member of the Board of Elders, sits on the equity task force for the Great Springs Project. The trail can help Indigenous people in Central Texas regain their access to the springs, she says. Because the Great Springs Project is working directly with city and county governments, “it gives us a voice at a table that has a lot of influence.” She says cities have often refused to make exceptions for Indigenous people to use the springs for ceremonies, saying: “ ‘Well, if we make an exception for you we will have to make it for everybody.’ But that’s not legitimate. You are making exceptions for us because you stole our land. . . . The fact that we now have a project that’s going to try to unite all four springs again as a sacred unified water entity, that’s really important to us.”