The valley floor of the Krom Antonies catchment consists of quaternary alluvial deposits. They cover a clay layer. In the West, East and South, the catchment is surrounded by a mountain system. These mountains are part of the Table Mountain Series, an Ordovitian to lower Carbonferous sandstone, which is mainly quartzitic. It is underlain by late Precambrian meta-sedimentary rocks, which are part of the Malmsbury group. The downstream areas of the Krom Antonies catchment are part of the Sandveld's quaternary to tertiary unconsolidated deposits. A granite pluton intrusion is located at the fault line crossing the catchment in Southwest–Northeast direction.

The soils are typically grey sandy soils. Nutritent values are low. They might be classified as lithosols and lithic soils on the steeper slopes and lime soils in the valley bottom.