Ha Ha Tonka is a classic example of what geologists call karst topography. Ground water dissolved a large cave system in dolomite bedrock millions of years ago. After regional uplift, lowering of the water table, and erosion of the land surface, portions of the cave roof collapsed. This created a chasm, several sinkholes, an island, a natural bridge, and an outlet for a large spring. The chasm and surrounding natural features resulted from this large-scale collapse. Subsequent erosion soothed the scarred landscape as soils accumulated and vegetation became established. The water of Ha Ha Tonka Spring pools behind small mill dams constructed in the 1830s, then flows into the Lake of the Ozarks, which was created in 1931.