Spencer Dinwiddie had 15 points and Josh Scott added 11 for Colorado (9-2), which is off to its best start since opening 9-2 in 1994-95.
The Buffaloes remain unbeaten in four meetings with Northern Arizona (4-6), a member of the Big Sky conference which dropped to 0-3 against Pac-12 teams this season. The Lumberjacks were beaten by Oregon and Arizona earlier this season.
DeWayne Russell had 15 points and Max Jacobsen 10 to lead the Lumberjacks, whose 47-point loss represented their largest margin of defeat this season. The previous high was a 43-point loss to Arizona.
Colorado was breezing by the break, taking a 57-21 lead while piling up a season high in points for a half.
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