Using Soil and Forest Type to Map Bedrock in Nemo, South Dakota

Bedrock mapping can be used to locate economic deposits, assess natural disaster (e.g., mass wasting) risk, and decipher the geologic history of a region. This study examines a site at Nemo, South Dakota to assess whether two contrasting types of bedrock produce different soil that result in different types of forest cover. Although bedrock varied, other soil forming factors were uniform. Within an approximately 1 km2 area, quartzite and metagabbro bedrock, ponderosa pine and quaking aspen forests were mapped. The soil above the quartzite bedrock is thinner and sandier and is dominated by ponderosa pine (Pinus ponderosa). In contrast, the soil above the metagabbro bedrock is thicker, mostly clay-sized and is dominated by quaking aspen (Populus tremuloides) and contains irises (Iris germanica). The increased CEC, phosphorus content, and clay content of the metagabbro-derived soil may account for the corresponding quaking aspen forest as aspens require more nutrients than ponderosa pine. Ponderosa pine is more tolerant of nutrient deficient conditions such as the quartzite-derived thin, sandy soil. This research indicates that because bedrock type influences soil properties which in-turn influence forest type, that forest type can be an additional tool in mapping bedrock contacts