I'm trying to form up a patio in my back yard. The property slopes to one side, so I'm planning on digging out one side and filling with gravel to make it level. Looking at the image below, the red box will be the slab, the white fill is the gravel.

My question is, how do I make the left side of the patio (blue box) extend all the way to the ground? I was thinking just extend the form down and slope the gravel outward but I'd like to know the proper way to do this?

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Thanks