Hello Sharon, the material on the back wall is a travertine. We used a paver just like the patio and set it as the wall facing as well. It is varied on its depth to give the wall some dimension and shadowing. As for the pool, it is about 28' long (not including the spa). About 14' wide at its widest and about 11' at the narrow middle. Let us know if you have any additional questions. Thanks!