The QuickSurfaces plugin for Autodesk® Civil 3D® provides an easy way to extract multiple “child” surfaces from an existing surface by selecting polylines that define their outer boundary. The plugin assigns the child surfaces a user-specified style and extracts terrain information, including mean slope, mean elevation, and minimum and maximum elevations. The user has the option to create child surfaces or just extract terrain information.
Note: This app uses a custom installer (and not the standard App Store installer).
You can download a free trial of this app here: https://www.vantecsolutions.com/product/quicksurfaces/