Small reefs at Grafton developed in a shallow water, high-energy environment. Evidence for this includes cross-bedded pre-reef deposits, cross-bedded interreef deposits with oncolites, and limited vertical thickness of reefs.
Larger reefs between Milwaukee and Thornton developed in a deeper, quiet water environment. Evidence includes heavily burrowed, mud-grade pre-reef and interreef deposits. Substancial vertical thickness of reefs and inclined flank beds indicate that the reefs grew upward under waters tens of meters deep.