The downtown core is not flood-prone, but the levee and Leonor K. Sullivan Blvd. The River des Peres floodplain includes portions of the Carondelet, Patch and Boulevard Heights neighborhoods, as well as parts of Willmore and River des Peres Parks. Although the City does not have many rocky bluffs over the Mississippi, locations like Chain of Rocks Park, Bellefontaine Cemetery, O'Fallon Park, the Archgrounds, and Bellerive Park are positioned high enough to provide panoramic vistas of the Mississippi and the American Bottoms in Illinois. In general, the limestone formations extend from the Mississippi bluffs west to Kingshighway Boulevard, and further west in some areas. These limestone formations contain many caves and sinkholes.
Some sinkholes lead into underground springs, resulting in the formation of sinkhole ponds.
Clifton Park Lake in the Clifton Heights neighborhood is one notable example. Carondelet Park also contains many sinkholes. Also, the development of clay mines and coal mines in South City resulted in occasional cave-ins and sinkage, because of the relative instability of limestone when it is undermined. The portion of the city west of Kingshighway and generally north of River des Peres, as well as the Baden and North Pointe areas, rest upon the more stable sandstone. The lower River des Peres valley in the Patch neighborhood and the lowlands near the Mississippi River east of Hall Street in the North Riverfront area rest upon alluvial deposits formed from frequent flooding.