Roman Polanski didn't actually cut Jack Nicholson's nose with a knife, but they got tired of explaining how the trick knife worked and spread the rumor that he really did it. And that's how legends are made, folks. (Source)

If Robert Towne had completed his planned trilogy he would've inadvertently summoned Captain Planet. After all, what better or more obvious way to structure a trilogy than basing each film on one of the four classical elements? Chinatown was water, and the sequel, The Two Jakes, was fire. But everyone hated The Two Jakes, so the third movie, Gittes vs. Gittes, was never made. (It would've been related to air.) (Source)

You did what, Old Sport? Robert Towne turned down a $125,000 offer to adapt The Great Gatsby for the screen. Instead, he asked for $25,000 to write Chinatown. (Source)

Ironically, the screenwriter wanted a "Hollywood ending." Robert Towne's original screenplay for Chinatown had a happy ending, but Roman Polanski insisted on changing it. (Source)

Hollis Mulwray simply would not give a dam—to the people, when they demanded it. But his real-life counterpart, the water department chief, William Mulholland, definitely did…and it broke. The Van Der Lip Dam collapse mentioned in the movie is based on the St. Francis Dam collapse, which killed 476 people. (Source)