Use this procedure to change the lower extension of any elevation connected to the elevation line. You can change the lower extension of the elevation line before or after you create a connected elevation. If you change the lower extension after creating the elevation, you need to update the elevation to show the changes.
You can also change the lower extension of an elevation using the Properties palette.
If you use model extents, the default for the lower elevation is 1 foot below the XY plane.
Viewing Elevation Grips in 3D View