Chandler’s Marlowe novels take place in Los Angeles and “Bay City” (Santa Monica). My annotated version of The Big Sleep explains the historical importance of Wilshire Boulevard:
A historic and even prehistoric route, once traveled by the Pleistocene animals that ended up in the tar pits at La Brea, Wilshire was widened in 1924 as part of developer A. W. Ross’s scheme to move shopping away from the traffic-choked downtown.
The expanded Wilshire was emblematic of the newly auto-centric city: it could accommodate six lanes of traffic, had synchronized traffic lights, and funneled automobiles to a brand-new shopping district (named Miracle Mile in 1928) where each building had its own parking lot.
They didn’t foresee the high cost of free parking.