...
Topography (transparent layer) and circle in XY and XZ views
To trim the terrain we will extrude cylindrical surfaces and use them for intersection
Utilities->Copy...
A translation of 3000 m in z, extruding surfaces
Copy with extrusion
And calculate numerically the intersection of surfaces with:
Geometry->Edit->Intersection->Surfaces
Try to select the minimum surfaces possible, because will find the intersection of the selected surfaces all against all, and it could be very expensive in time.
Selection of surfaces to be intersected