The ISO grid
The California ISO manages the flow of electricity for about 80 percent of California, which encompasses all of the investor-owned utility territories and some municipal utility service areas. There are some pockets of California where local public power companies manage their own transmission systems.
The ISO is the largest of about 40 balancing authorities in the western interconnection, handling an estimated 35 percent of the electric load in the West. A balancing authority is an entity responsible for operating a transmission control area. It matches generation with load and maintains electric frequency of the grid.