James Ellroy’s editors let him down a few times in the early chapters of American Tabloid. HUAC refers to the House Committee on Un-American Activities, not the “House Committee on Un-American Activists” (ch. 4, p. 42). Chapter 8 is set on 11 December 1958, a couple years before Interstate 95 saw any traffic in Florida, and yet Kemper Boyd drives I-95 out of Miami. And Lenny Sands drives north out of Chicago in chapter 12 (on Sheridan Road? on a yet-to-be-built freeway?) “past Glencoe, Evanston, and Wilmette” (p. 100) on the way to Winnetka. The correct south-to-north ordering of these north shore suburbs (with a few others in between) is Evanston, Wilmette, Winnetka, Glencoe.
Ellroy does use an interesting slang term (twice) whose meaning is not immediately obvious from context.
Pete saw the Chevy’s taillights. Fulo floored the gas and rammed them. The car swerved off the road, clipped some trees and stalled dead.
Fulo brodied in close. His headlights strafed Kirpaski—stumbling through a clearing thick with marsh grass. (ch. 7, p. 64)
Brody (n.) is glossed as “intentionally spinning in circles and sliding in an automobile” with related words doughnut and 360. Unfortunately, it’s a common surname so an online search for other appearances is difficult.