As rain continued to fall, the slightly acidic rainwater dissolved the limestone. As limestone wore away, the groundwater came into contact with the land surface and created a massive wetland ecosystem.[36] Although the region appears flat, weathering of the limestone created slight valleys and plateaus in some areas. These plateaus rise and fall only a few inches, but on the subtle South Florida topography these small variations affect both the flow of water and the types of vegetation that can take hold.[38]