the mountains and the canyons started to tremble and shake

On 9 February 1971 the Sylmar earthquake hit the San Fernando Valley in the early morning, and later that day Jimmy Page flew into Los Angeles with engineer Andy Johns to mix an album that already contained a song about California shaking itself apart. Aftershocks were still arriving. Page listened to what he had on tape, heard Robert Plant sing about the mountains and the canyons starting to tremble, and quietly decided to mix that one last — no point, as he saw it, in tempting the ground twice. Johns told him not to be so bloody stupid.

It had been cut at Headley Grange, the damp Hampshire poorhouse where the band worked with nothing to distract them, and it went out on the untitled fourth album that November under a name it grew into: the working title was “Guide to California”. There is no drum kit anywhere near it. Page plays six- and twelve-string acoustic in double drop D, both E strings slackened a whole tone so the chords sit lower and looser than the shapes suggest, and John Paul Jones, who spent most of his career holding down the bottom end, plays mandolin over the top with the light, slightly nervous tremble that instrument does when nobody is asking it to be loud.

The girl in the song is not really a girl. Plant, twenty-two when he wrote the words, is chasing an idea that was living in Laurel Canyon at the time, and the last verse reaches straight into Joni Mitchell’s Song to a Seagull to find her. Page was open about it: he told Rolling Stone in 1975 that Mitchell was what he played at home, that she could stand back from a thing that had happened to her, crystallise it, then write it — “She brings tears to my eyes. What more can I say? It’s bloody eerie.” Plant, decades on, told Spin the lyric was a bit embarrassing but that it summed up who he was at twenty-two. Both things are true at once, which is the whole appeal. Put it on and let a very loud band be quiet for three and a half minutes.