The Citronelle Formation is a geologic formation across the Gulf Coast of the southern United States, occurring in Alabama, Florida, Mississippi, and Louisiana. Rather than a single landmark, it is a widespread body of rock and sediment. Identified as Hemphillian in age, it is significant for preserving fossils and for the research those remains have supported. Studies associated with the formation include work on Pliocene three-toed horses from Louisiana, highlighting both its paleontological importance and the long-running effort to understand its age and origin.