Pearblossom Highway was a landmark work of photographic art, but you will not find it in standard histories of photography. I don't know why. Every photographer should have a good look at this picture, because it challenges and overcomes many of the weaknesses in photography. He has manipulated the perpsective of the composite by photographing from a multitude of viewpoints, usually quite close in, sometimes using a ladder.
I came across this rare video of Hockney talking about the picture on YouTube, recently posted by the Getty Museum. Hope you find it interesting.