They were nerds. Dorks. Lonely mouth-breathers who sat in the back of the classroom. And the others were bastards, manipulators, egomaniacs who never met a woman they couldn’t (try to) seduce or a drug that couldn’t seduce them. Easy Riders, Raging Bulls: How the Sex-Drugs-and-Rock’n’Roll Generation Saved Hollywood, Peter Biskind’s great, scathing, news-packed history of the ways in which the finest directors of that fine film decade, the 1970s, had it and then lost it, is going to shatter anyone who still believes that unforgettable movies emerge, fully realized, from the storyboards and barked orders of artistic geniuses. For the rest of us, though, this book is one hell of an elixir — salty with flavorsome gossip, sour with the aftertaste of misspent careers, intoxicating with one revelation after another, and bitter with decades-old grudges (the late producer Don Simpson on Robert Altman: ”A true fraud…a pompous, pretentious a–hole…a f—ing drunken disaster”; Altman on Simpson: ”I’m only sorry that he didn’t live longer and suffer more”).

By the late 1960s, Hollywood was buckling under the freight of overproduced, budget-busting garbage (sound familiar?), and as Biskind persuasively demonstrates, two different generations of directors were itching to take over. The revolution that resulted in a sunburst of great films was largely led by guys who felt their time was running out. Arthur Penn was 45 when he made 1967’s Bonnie and Clyde, and in 1970, when he scored with M*A*S*H, Altman was already 45 and beginning the second act of a previously undistinguished career. That year, Steven Spielberg was just 23 and George Lucas 26. A few years later, they’d make Jaws and Star Wars, seedlings of the current blockbuster era that ironically turned studios into such monolithic money machines that the next film revolution had to come from the world of indies.

Biskind brackets his book with close looks at Bonnie and Clyde (1967) and Raging Bull (1980), and it can’t be an accident that he’s chosen a pair of masterpieces about the pathology of self-destruction to bookend the decade. Take a look at Francis Ford Coppola, who torched epic amounts of time and scads of money on the creation of failed mini-studios after The Godfather. Or Hal Ashby, who made Shampoo and Coming Home and then became consumed by feuds and pharmaceuticals. Or William Friedkin (The French Connection), Bob Rafelson (Five Easy Pieces), and Peter Bogdanovich (The Last Picture Show), who made a couple of good movies each, treated people disgracefully, and were already skidding toward the off-ramp by the time Gerald Ford took office. What went wrong? ”Arrogance and p—y,” says Friedkin, who isn’t far off the mark. Cocaine practically flurries across each page. No wonder the book’s last chapter is called ”We Blew It.”

Biskind knows that what derailed so many of these careers is worth mourning, beyond its lurid car-wreck fascination; his research is so scrupulous and instructive and his passion for movies so unquestionable that his clear contempt for the excesses of the men he writes about makes sense — after all, they trashed their own gifts. But the signal achievement of this archaeological dig of a book is that Biskind also cares about what went right — the movies. To read his accounts of the making of The Godfather, Taxi Driver, Chinatown, Jaws, and Easy Rider (just the tip of a remarkably deep list) is to understand what no movie history has ever shown as vividly: Masterpieces are accidents, and careers are bizarre trajectories of happenstance, lucky convergences, missed opportunities, furious compromises, technical difficulties, and blessings in disguise. Talk all you want, for instance, about Spielberg’s shrewd underuse of the shark in Jaws, but it helps the discussion to know that you see that shark so rarely in part because it looked phony and its eyes kept crossing by accident.

Spielberg, by the way, is one of the few directors who doesn’t come off as a walking disaster area in Easy Riders, Raging Bulls. Scorsese, smart and insightful, is another. (Young directors in need of moral instruction should note that their careers are both still thriving, so the story does have a moral of sorts: Be a nerd, not a bastard.) As for many of the rest, in the words of one survivor of the era, ”directors…are among the worst people we’ve got.” Okay, so you wouldn’t want to know them. But if, after reading this book, you don’t race to the video store, you will have missed the point: Years later, their movies are still awfully good company. A