How do I project 2D surfaces with assigned materials onto topo?

I have modeled subregions for a site model in 2D based off of a 2D CAD file. I imported the same CAD file in 3D below this 2D surface and want to project/drape/copy these surfaces and their materials down onto the topo so that they adopt its contours. How can I do this quickly and easily?

See screenshot below for visual explanation.

Is this the sort of thing you are trying?

Yes, but I have a lot of geometry and topo triangles involved so I’m trying to avoid having to use the paint bucket to fill ALL of these surfaces with the same materials again.

Have a look at Super Drape it may do what you want.