Now create more wedges on the inside of the circle but line them up with the sides. At least one vertex of each WEDGE created should be connected to one of the vertices of the side or else, that wedge is not neccessary.
Vertex manipulate them to line them up. Then, using vertex manipulation, slope down the wedges by connected the vertices of each wedge that ARE NOT already adjacent to the side. The picture will explain it better:
Step 4:
You're almost done...If you don't have much room for more wpoly, you can select all of the wedges inside the box and turn them into func_walls so they dont cut up any other brush. But that is not really necessary because they do not raise the rspeeds much to begin with.
Texture all of the sloped wedges and the ground brush of the crater with an appropriate ground/dirt/blast crater texture. And voila, you're done with your crater!
Additional Notes:
If you need more than one crater in your map, you can just copy and paste a crater. Just be sure to change the size and shape of the crater so they don't all look the same.
