Soil is the foundation for the entire ecosystem of an area. Soil affects the plant life that grows in an area which, in turn, affects the wildlife that can reside there. Soil type is influenced by the parent material (or underlying rock) from which it was formed. Soil is also affected by topography, plant and animal life, time, and climate. All of these factors tell us how the soil was formed and what kind of life it can sustain.

Monocacy has many different soil types but two basic rock types below. Along the Monocacy River and northward the soil has a limestone base. Limestone soils are generally very fertile which is good for the agriculture of the area. Also, the basic quality of limestone tends to neutralize acid rain making it good for native vegetation and water quality.

The southern region of the park consists of many hills and ridges with soil that is derived from a slate parent material. The layer of organic material in this soil is very thin, below which is a thick layer of slate which prevents vegetation from rooting deeply. During storms the shallow rooted trees often blow over causing forest gaps.