Sloan also became a session guitarist as part of the group of L.A. session musicians known as The Wrecking Crew, working with such well-known backing musicians as drummer Hal Blaine, guitarist Tommy Tedesco, bassist Joe Osborn, and bassist/keyboardist Larry Knechtel, among others. While working with Barry McGuire, Sloan created and played a guitar introduction as a hook to a new song by John Phillips entitled "California Dreamin'", and the same backing track was used for the hit version by Phillips' group The Mamas & the Papas, which led to Sloan being a regular in their recording sessions. Sloan generally played the lead guitar tracks on most of the songs he wrote, including the famous riff in "Secret Agent Man".