Horizon letter for bedrock What is the official letter for the bedrock soil horizon? I know that the letters to represent the A, B, and C horizons are widespread, but the fourth layer (bedrock) is referred to with different names. Some call it the D-Horizon, some the R-Horizon, and some just say bedrock. Is there any standard or official term, and if so, what is it?
According to Wikipedia and Nature.com, "R Horizon" is the official letter for bedrock.



CAPTION: Example soil with designations that communicate the soil formation processes occurring in each horizon.