The basic soil classification by USDA uses letters to designate different divisions of the land underneath. The letters used were O, A, E, Bt, C, H, and R. These letters pertain to different parts of the Earth's crust.
Bedrock is the layer of undisturbed rock and other formation that lies below the soil and/or other materials. This layer is usually unexposed except for those areas which are usually affected by erosion.
The letter used to designate bedrock is letter R. The answer to this item is letter C. R.