Geologically speaking, Jones Valley is a dynamic place to live. Due to its karst topography, sinkholes threaten to open at any moment, springs burst from the ground, and there are underground caverns beneath our feet. Several rock formations form the karst floor of the valley, and two of them are found at Roebuck Springs.
The spring emerges exactly along the boundary between the Conasauga Formation and the Ketona Dolomite Formation. The Conasauga is a bluish-gray limestone with intervening layers of dark-gray shale. Its rocks formed 501–513 million years ago, in the mid-Cambrian Period. At this time, most of Alabama was submerged in the tropical waters of the southern hemisphere. You can read more about the Conasauga Formation in the geology summary for the McWane Science Center on Trek Birmingham. None of this limestone is visible at the surface at Roebuck Spring.
The Ketona Dolomite (or dolostone) is a light-gray rock that outcrops near the entrance to the recreation center. This rock layer is slightly younger than the Conasauga Formation but also dates back to the mid-Cambrian. Like limestone, dolostone dissolves slowly when exposed to acidic waters.
What triggers the formation of dolostone is a mystery to geologists. They suspect that most probably formed indirectly as magnesium replaced calcium in limestone that had already formed. However, geologists cannot find examples on today’s earth where this process is occurring. Thus, the origins of thick dolostone deposits, like the Ketona, remain unexplained. The only clue they have is that dolomitic muds can form in very salty tropical lagoons where it is created as a by-product by certain algae.