"Down wash" as a source for mineral particles in the soil

Question

In a previous IGCSE examination paper$^1$, the following question was asked and answer provided:

State one source of mineral particles in soil.

Marking Scheme:

Accept any one of:

1. rock;
2. down wash;

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What's "down wash" and how is it responsible for providing minerals to soil? Googling the term lead me to an aerodynamics definition, which I doubt is the one referred to by the marking scheme.

$^1$ UCLES. Environmental Management, 0680/12, Paper 1. Cambridge International General Certificate of Secondary Education, February/March 2017.

Answer 1

Downwash can be part of some erosion environments where minerals are moved down from their host rock environment to another location.

Black Snake Range - Granite Slopes, Victoria, Australia

The crest of the divide rises to almost 400 metres and at this site there are numerous exposed granite slopes and large boulders near the ridge crest. The lower slopes have a cover of granite downwash and the minor valleys have become partly infilled with this granitic sand wash, and hence they are swampy

Southdowns, UK, page 4

Overlying the bedrock geology are drift deposits of alluvium (along the numerous streams) and ‘head’ (downwash deposits at the base of the Greensand Hills around Liss and Petersfield).

In the Discussion section of Slope Stability and Slope Formation in the Flysch Zone of the Vienna Forest (Austria)

The downwash of the basal clays and marls, uncovering the solid bedrock, has to be regarded as the main aspect of this phase