Three dominant soil types are found in Forest Park: Cascade, Goble and Wauld.

The Cascade and Goble soils, often referred to as Portland Hills Silt, have similar physical characteristics, capabilities and limitations. They differ slightly in two basic characteristics: Cascade soils are generally found on the broad rolling ridgetops of the park, formed from windblown silt deposits. The Goble soils, formed from windblown silt and volcanic ash, usually occur on hillisides and ridges.

The Wauld soil is substantially different from the Cascade and Goble soils. It contains a higher proportion of clay in the subsoil and is very rocky. This soil is generally found at the base of steep hill slopes and drainage side-slopes. Its steep, shallow, rocky characteristics contribute to a moderate windthrow hazard.