retaining walls cut out of a topo site model

[pdxdan11]

i have cut a face representing a retaining wall out of a topo model after performing a boolean from a spline object, named it as a separate object, now i want to extrude it up 4 feet. once the topo has the edit mesh modifier applied in order to cut the shape of the wall out of it i can no longer extrude. i would like to know how to extrude the shape. what function or modifier would i need to use? or should i try something else? i already tried to shapemerge the spline but that didn't work either. i have read several chapters in the 3ds max2009 bible and still can't find the answer. i am stuck! can anyone help? i know this has to be simple. thanks.

[Cad64]

Your explanation is confusing, but if you want to Extrude parts of a surface that has an Edit Mesh modifier applied to it, just expand the Mesh modifier and select Polygon.