The Wrecking Crew was a group of studio musicians in Los Angeles in the 1960s who played on hits for the Beach Boys, Frank Sinatra, Nancy Sinatra, Sonny and Cher, Jan & Dean, The Monkees, Gary Lewis and the Playboys, Mamas and Papas, Tijuana Brass, Ricky Nelson, Johnny Rivers and were Phil Spector's Wall of Sound. The amount of work that they were involved in was tremendous.
They were also involved in groups that I like to call the Milli Vanillis of the day. A producer would get the guys in and lay down some instrumental tracks. If it became a hit, they would record an album and put a group together to go on the road. This happened many times with groups like the Marketts, Routers, and T-Bones. The next day they would do the same thing and call it another name. Same musicians, but different group name.
The record industry was primarily in New York, London and Detroit in the late '50s and early '60s. Then there was a surge towards the mid-60s that pushed the recording to the West Coast. So these musicians were recording around the clock for a good 8 years. The heyday for this group was in 1967 when the charts turned to the West.