Proulx criticizes Oscar voters and the Academy Awards ceremony in the 1,094-word rant, which appeared in Saturday's issue of The Guardian, a liberal paper boasting 1.2 million readers daily.
The best-picture Oscar went to "Crash," which focuses on race relations in Los Angeles.
Academy members who vote for the year's best film are "out of touch not only with the shifting larger culture and the yeasty ferment that is America these days, but also out of touch with their own segregated city," Proulx writes.
The 70-year-old Pulitzer Prize-winning author points out that "Brokeback," which was nominated for eight Academy Awards, was named best picture at the Independent Spirit Awards one day before the Oscars on March 5.
"If you are looking for smart judging based on merit, skip the Academy Awards next year and pay attention to the Independent Spirit choices," Proulx advises.
She even lashes out at Lionsgate, the distribution company behind "Crash."
"Rumour has it that Lionsgate inundated the academy voters with DVD copies of Trash, excuse me, "Crash" a few weeks before the ballot deadline," Proulx writes.
She decries the "atmosphere of insufferable self-importance" inside the Kodak Theatre, the Oscars site, and describes the audience as a "somewhat dim L.A. crowd." The show, she writes, was "reminiscent of a small-town talent-show night."
"Clapping wildly for bad stuff enhances this," Proulx writes.
She notes that "Brokeback's" three Oscar wins, for original score, adapted screenplay and direction for Ang Lee, put it "on equal footing with King Kong."
When Jack Nicholson announced "Crash" as the best-picture winner, "there was a gasp of shock," Proulx writes.
"It was a safe pick of 'controversial film' for the heffalumps," she writes, using the elephant-like "Winnie the Pooh" character to describe Academy voters.
"For those who call this little piece a sour grapes rant," Proulx concludes, "play it as it lays."
Calls by The Associated Press to Proulx's Wyoming home and her literary agent, Elizabeth Darhansoff, were not immediately returned Tuesday.