At which Los Angeles studio was most of Metallica recorded?

Most of Metallica was recorded at One on One Recording Studios in Los Angeles.

Metallica began recording there in October 1990, working on the album over an eight-month period. The sessions continued through June 16, 1991, with the band and producer Bob Rock refining arrangements, performances, vocals, and guitar sounds in a demanding studio environment.

The group also spent about a week at Little Mountain Sound Studios in Vancouver, British Columbia. Additional overdubs and mixing took place at A&M Studios in Hollywood. These extra locations are why One on One is best described as the principal recording studio rather than the only facility used.

The One on One sessions marked a change in Metallica’s working method. Rock wanted the musicians to play more like a unit, creating a more immediate and polished sound than on the band’s previous records. The finished album was released by Elektra Records in August 1991.