Here's why:

* Talus is a collection of broken rock fragments (also called scree or debris) that have accumulated at the base of a cliff, slope, or mountain.

* Bedrock is the solid rock that lies beneath the soil and other loose materials.

* Horizon is a layer of soil or rock that is distinct from the layers above and below it.

So, a horizon containing large pieces of broken-up bedrock is likely a talus slope, where weathering and erosion have broken down the bedrock and gravity has transported the fragments downhill.