Get out photoshop. Paint a displacement map, like the one below
Then, create a NURBS plane, about 10 spans by 10 spans.
Go into hypershade
Create->2D Texture -> File and open the map.
create a new material.
Right click the file with the displacement map and right click drag over to the material. Then choose displacement map as the input.
Now, this part is optional.
Select the plane, and go to convert-> displacement map to polys.
This will take up several hundred thousand polys, depending on the density of your map.
Render- heres my result:
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