1983 Chevy Frame Question

[apbmalibu]

I just looked at an 83 Chevy short box 2 wheel drive. When I was under it, I noticed that right where the catalytic used to be, the bottom of the frame dips down. The top part of the channel is flat, but the bottom part sort of bows down. Is that factory? It doesnt have any marks where someone would have pounded it down or anything, but looks sort of out of place. Does anyone know what I'm talking about? Instead of the lower part of the frame rail being at a 90 degree angle, it dips down.