A carbonate shelf started to develop over the sandy mudflats early in Paleozoic time. Sediment accumulated on the new but slowly subsiding continental shelf all through the Paleozoic and into the Early Mesozoic. Erosion had so subdued nearby parts of the continent that rivers ran clear, no longer supplying abundant sand and silt to the continental shelf. At the time, the Death Valley area was within ten or twenty degrees of the Paleozoic equator. So the combination of a warm sunlit climate and clear mud-free waters promoted prolific production of biotic (from life) carbonates. Thick beds of carbonate-rich sediments were periodically interrupted by periods of emergence, creating the (in order of deposition);