I know it is hard to tell from the picture, but all of Rusty's hard work with the tractor is sliding with the mud. With the heavy rain that we had Friday and the snow Saturday, the mud started giving way to the hole where the pond was. Rusty had to take the pond out because the weight from the water and the mud sliding, it was starting to warp the pond (it's plastic).
So, to prevent further sliding, Rusty used this stuff to help hold up the rocks until he can rearrange the waterfall rocks. It's a bummer.