Adding Slope to a vertical space

Here I am adding slope with vertical plaster castings hot glued into place with plaster backfill. Then I trowel in Sculptamold modeling compound, let set for a few minutes then come back with a wet paint brush and water to smoothen out the material. I realize I have to add quite a bit more Sculptamold to get much taller and full alluvials. You can see where I am talking about, the horizontal areas that look like swooping roads, I will build these areas up to create more slope. I went ahead and painted, aware that I will need to come back and finish the alluvials at a later time. I plan to add loose soil and rock to the slope and add dried field grasses to complete the scenery here,