The city of Fontana, California

When/How/Why did Jurupa Peak get flattened?

The high point of Jurupa Hills has a flat surface on the peak as a result of some manual flattening, probably many years ago. Does anyone know the true when/how/why of the reason for the flattening? I've heard speculation that it was prepped for military or radar installation that never subsequently happened or that it was somehow connected with the Ontario Airport. While those speculations sound plausible they give no clues about when the flattening happened. Does anyone know any details? It could have been flattened in the 1940's for all I know or maybe the 1980's.