It is mostly caused by particulate matter in the air. Not so much pollution from California, though I'm sure a bit of it is. More likely to be dust and our own pollution.

is there a citation for that?

the reason i ask is the parent comment talks about the scattering of light at sharp incidence levels favoring certain wavelengths, with the reds being what naturally is dominant at dusk and dawn light-hitting-atmosphere angles.

Looked through a few pages, this one I think explains it fairly well https://demos.smu.ca/index.php/demos/astronomy/35-red-sunset...

The answer it gives is more of a combination of what I thought and what the parent said, tl;dr version: scattering both due to just normal oxygen and nitrogen composition of the air and also pollutants (which I think dust would also qualify, though most things I could find that specified were talking more about sulfur compounds).

Neat!