If you could peel away the tops of the hills in the Barton Creek recharge zone like the skin of an orange, you would find quite a few holes. The limestone beds that comprise the Edwards Aquifer are full of cavities carved over millions of years by underground rivers and streams.
Many of the cavities are filled with water. Some of the cavities act as conduits, or tunnels, and feed water to Barton Springs.
But other cavities are relatively dry. They form a network of caves – at least 24 in all – that underlie the Barton Creek watershed. Some of the caves are remnants of ancient conduits, while others were gouged from the sheer cliffs by creeks.
Most of the caves are less than 400 feet long – about the length of a football field, measured from end-line to end-line. But the largest, named Airman’s Cave, is at least 12,000 feet long, making it the eighth longest known cave in Texas.
The caves of Barton Creek are home to many fascinating creatures that have adapted to life in the subterranean world. Airman’s Cave, for example, houses a new species of harvestmen (a relative of the spider) much like the Bee Creek Cave harvestman, which is on the federal endangered species list. Cave X, another major cave in the basin, contains a rare species of blind cave millipede.
Scientists have recently recognized that dozens of rare species of cave animals live in different geological zones near Austin. Barton Creek appears to be a barrier between zones. Many of the rare species found in these caves evolved over hundreds of thousands or millions of years in isolated cave “islands.”
We are still learning to understand these cave ecosystems. One thing is certain though: each depends for survival on unpolluted water from the surface.