public ElevationSurfaceLayer GetGroundElevationSurfaceLayer()

{
    //Define a ServiceConnection to use for the new Elevation surface
    var serverConnection = new CIMInternetServerConnection
    {
        Anonymous = true,
        HideUserProperty = true,
        URL = "https://elevation.arcgis.com/arcgis/services"
    };
    CIMAGSServiceConnection serviceConnection = new CIMAGSServiceConnection
    {
        ObjectName = "WorldElevation/Terrain",
        ObjectType = "ImageServer",
        URL = "https://elevation.arcgis.com/arcgis/services/WorldElevation/Terrain/ImageServer",
        ServerConnection = serverConnection
    };
    //Defines a new elevation source set to the CIMAGSServiceConnection defined above
    //Get the elevation surfaces defined in the map
    var listOfElevationSurfaces = map.GetElevationSurfaceLayers();
    //Add the new elevation surface 
    var elevationLyrCreationParams = new ElevationLayerCreationParams(serviceConnection);
    //Note: needs to be called on the MCT
    var elevationSurface = LayerFactory.Instance.CreateLayer<ElevationSurfaceLayer>(
        elevationLyrCreationParams, map);
}

{
    // retrieve the elevation surface layers in the map including the Ground
    var surfaceLayers = map.GetElevationSurfaceLayers();

    // retrieve the single ground elevation surface layer in the map
    var groundSurfaceLayer = map.GetGroundElevationSurfaceLayer();

    // determine the number of elevation sources in the ground elevation surface layer
    int numberGroundSources = groundSurfaceLayer.Layers.Count;
    // get the first elevation source layer from the ground elevation surface layer
    var groundSourceLayer = groundSurfaceLayer.Layers.FirstOrDefault();
}