"Cossacun" isn't even a word.
I'm pretty sure there are a lot of references to US highways and routes, but as far as I can make out, the actual lyrics to that part are:
"Up on the 405, skiddin' on the 101
We 69-in' on the 66 across the coun...
trees, and autumn leaves, kneeling right before the sun
And when the night and moon are (?) another day's begun"
Honestly not sure what that word is in the last line but the rest is accurate.
The lyric in the second line is suggestively referring to Kesha's
gold trans am, before turning
that word into countries, by means of trees, and autumn leaves. I've always known this tho, I never knew it was such an obscure lyric to some.

It's like in Dear Future Husband when Meghan rhymes "bed" with "kisses" instead of "head".
