This was true at one point in time, in particular, with the Rogue River Ford plant, which was pretty amazing. Iron ore, raw material for making glass, and the like--all done there.
For good or bad, this is no longer how it works. Entire subassemblys are outsourced.
Hyundai are advertising that they have an ultra-modern (relatively) environmentally friendly steel plant in order to lower GHG emissions and control quality.
An interesting play.
I had a chance to visit it before they stopped the tours. The most impressive part was the plant where they took in a huge chunk of steel and heated it red hot, then repeatedly rolled it until it was thin, then rolled it up.
For good or bad, this is no longer how it works. Entire subassemblys are outsourced.