What type of bedrock is defined as weathered or soft?

The correct answer reflects the characteristics of the R horizon, which refers to the layer of bedrock found beneath the soil layers. The R horizon can indeed consist of weathered or soft rock, representing the boundary where intact bedrock begins, yet it may not be in a solid, unweathered state. This can include various types of rocks that have undergone processes such as weathering, which breaks them down and softens them over time.

When discussing bedrock types, it is essential to differentiate among the various horizons and their physical attributes. Hard bedrock typically refers to solid or unweathered rock that is not easily broken down. Weathered bedrock is a term that could describe conditions similar to the R horizon but is not the designated term for specific soil classifications. Soft sediment generally refers to unconsolidated materials that have not yet transitioned into bedrock and thus do not fit the definition being sought in this question.

Understanding soil horizons and their characteristics helps in evaluating soil profiles and their suitability for various applications, including construction, agriculture, and environmental assessments.