At the Buchan karst in southeastern Australia, Early Devonian carbonates contain >700 caves and karst-related features. The Potholes, in the northern part of the karst, is a densely cavernous area with >100 caves and 60 dolines over only ~0.8 km2. The caves here are predominantly vertical and the roofs commonly show smooth upward steps, indicative of having formed by rising groundwater. Because of sea level fluctuations during the Early Devonian, the limestone at The Potholes forms a tongue that lenses out to the south and is overlain and underlain by relatively insoluble marl. Mapping of fluvial sands and gravels and valley-filling basalt shows that in the Paleogene, the limestone lay beneath a broad, southwards-flowing river valley. Cave development occurred along phreatic loops within the limestone underneath the riverbed, and the upwards limbs of these phreatic loops were focussed into a small area where the limestone lensed out. The concentrated upwards groundwater flow, which connected to springs in the riverbed, resulted in intense cave development within a restricted area, where the groundwater exploited many different pathways within the limestone. The Potholes caves developed entirely beneath the riverbed, and are notable in that numerous caves fed multiple resurgences rather the more common situation world-wide of a single passage connecting to a resurgence. Both these characteristics reflect the unique geological configuration of the site, and show how karst development is determined by the particular arrangement of soluble limestone beds.Dissolution of The Potholes caves could have begun in the mid-Cretaceous, when uplift increased the gradient of the ancestral river flowing over the limestone, driving groundwater flow through phreatic loops beneath the river, and terminated when the caves were drained following a second uplift in the mid-Pliocene. This demonstrates the antiquity of cave formation in this part of Australia.