From the soil surface, you are saying 6" of the soil is white?

Or, that there is a 6" layer of white soil at some greater depth in the ground?

When I moved here years ago I discovered that about 18" down from the surface, there is "caliche." It is a harmless mineral deposit associated with the depth winter snowmelt usually reaches before evaporation slows and stops it from going deeper. Repeated year after year, dissolved minerals form a layer, sometimes binding rocks together.

This idea might be far afield from what you have noticed.

Steve

A picture would be helpful though it sounds like fungus. Probably nothing to worry about. Healthy soils should have fungus.

Confirmed as a fungus by extension office (due to deteriorating tree roots). Supposedly it won't hurt anything.