That is the e horizon which stands for eluvial. Spodosols form in acidic environments and this causes the iron and humus to move down the soil profile as a complex as rain moves through. So the black humus and red iron are removed which gives soil most of its color. What you are left with is the silt and sands that are the pale color you see.

Likely dug with a machine. The white material, my guess, is sand. Nutrient deficient highly draining sand. The dark and uneven horizon line is where what usually is a water table that holds drainage in place. In areas where that water level fluctuates, usually seasonally, you can wind up with this kind of stark line in the soil.

The uneven horizon likely is due to organic material, like tree roots, diving down through the sand and in many cases dying and decomposing underground.

But there are a number of spodosols and they’re formed a bit different from what causes em and I’m taking 10 year old coursework off the brain shelf to remember.