The soils in the park are identified as being in the Rocky Ford-Numa-Dorman Association along the Arkansas River. As recent alluvial deposits of the river, the soils consist of deep, nearly level, well drained clay loam soils mainly on upper terraces, or silty- clay, sandy soils on river bottom lower plains. The mature upper terraces exhibit a soil of thick, silty clay loam over silt loam subsoil.
The lower river terraces consist of nearly level, somewhat poorly drained, slightly saline, clayey to sandy soils. The parent layer is about 12 inches thick and is generally high in organic matter. These soils are subject to occasional flooding. The subsoil is slowly permeable and poorly aerated. Salt-tolerant plants such as saltgrass and alkali sacaton grow well on these soils.
def. alluvium clay, silt, sand, gravel or similar detrital material deposited by running water.