Groundwater moving through the Edwards limestone slowly dissolves openings in the rock. Some of these openings become caves large enough for human explorations.

Deposition of calcite flowstone

Deposition of calcite flowstone is commonly found in area caves and can take many terms and colors, all with unique characteristics and appeal.

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.


Blind cave harvestman

The blind cave harvestman is a rare species discovered in recent years. Harvestmen are arachnids but differ from spiders because they lack poison glands and a waist between the front of the body and the abdomen.


Millipedes have a formidable appearance, but are actually harmless. They lack poison glands and generally feed on fungus. Travis County contains six endangered cave species plus 26 other rare cave species that are highly adapted to their environment.

Stalactites and Stalagmites

Slowly dripping water sometimes deposits minute amounts of calcite on cave ceilings and floors. Slender, pointed stalactites hang “tite” to the ceiling, while stalagmites “mite” reach the ceiling someday.

Water dripping from stalactite

A single drop of water is not significant by itself. However, without it and the drops that follow, there wouldn’t be any caves, cave formations, aquifer or springs.