In 1965, the band began a period of heavy touring on the West Coast of the United States, finally signing to Capitol Records in 1967 and released Quicksilver Messenger Service, followed by Happy Trails. By this time, Murray and Duncan had left, and Nicky Hopkins joined in time for 1970's Shady Grove; Duncan returned soon after. This line-up lasted for one year, followed by more personnel changes until the group finally disintegrated. The band reunited in 1975, and again in 1986.
Quicksilver Messenger Service was also the name of a London-based firm of motorcycle couriers in the 1990s, almost certainly inspired by the name of the band.