Johnson drained a trio of 3-pointers for the Wildcats (13-0), who romped in their final tune-up before the start of their Pac-12 conference schedule.
Rondae Hollis-Jefferson, subbing for injured center Kaleb Tarczweski, struck for 14 points.
Brandon Ashley contributed 11 and nine rebounds for Arizona.
Aaseem Dixon led the Lumberjacks (3-8) with nine points.
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