"California" is a song by Joni Mitchell from her 1971 album, Blue
During the week of Blue
's 50th anniversary, Joni reissued the album and a lot of musicians expressed their adoration for it. Beck was one of them, posting a snippet on Instagram of him performing the song.
It was only a short segment, and Beck commented that he was "digging into the archives celebrating the 50th anniversary."
It is unclear exactly when he recorded, but my educated guess from the sound is it may have been around the time he also recorded a bunch of Nick Drake covers (2005). I believe he said he did as a sort of exploration into songwriting, to see how they worked, and wouldn't be surprised if he also dug into some Joni songs for that reason.
Release them please!