In which US city did Metallica primarily record The Black Album?

Metallica primarily recorded The Black Album in Los Angeles.

The main sessions took place at One on One Recording Studios in Los Angeles, where the band worked with producer Bob Rock from October 1990 into 1991. Additional work was completed at Little Mountain Sound Studios in Vancouver and at A&M Studios in Hollywood.

The Los Angeles sessions were notable for Rock's different production methods. He encouraged the musicians to record more collaboratively and sought a stronger live feel. The band also spent extensive time selecting and editing performances because of its perfectionist approach to recording.

The album's primary studio is sometimes confused with Little Mountain Sound, which was used for about a week, or A&M Studios, where later overdubs and mixing took place. One on One remains the principal recording location associated with the album.