Copy and Create an Editable Existing Profile
KaDe King of USCAD delivers the How to Copy and Create and Editable Existing Profile in Civil 3D.
From the Autodesk AKN Civil 3D Screencasts
See KaDe King's AKN page
KaDe shows how to solve that silly little Civil 3D sampled surface thing that drives some newbies nuts about copying and editing the existing ground.
Maybe you want to also learn the Best Fit Profile tools to clean the results up a bit more quickly too.