Some other articles, including ones from earlier articles with the sink hole:

• https://abcnews.com/video/134843285/

• https://www.nbclosangeles.com/news/local/west-hollywood-water-main-break/3919017/

• https://abc7news.com/post/west-hollywood-water-main-break-major-flooding-leaves-cars-streets-apartment-buildings-underwater-massive-sinkhole-opens/19521832/

It's a pretty big main (36") and was installed in 1916. I don't think I saw it referred to as a transmission main but at that size I would be surprised if it wasn't!