As the story opens a narrator recalls the character Paul Bunyan and his exploits and states that many people still question the giant's existence. Then he challenges to ask "a certain rabbit" whether he is real. Just then Bugs Bunny comes walking by touting a bindle and singing "Jimmy Crack Corn". He then comments on the unusual looking trees he passes, oblivious to the fact that they are abnormally large asparagus and that he has entered a rather large vegetable garden. He then finds an oversized carrot and lies next to it for a nap under the pretense that it is a boulder. However, he quickly rises up and points out that he smells carrots. Turning his attention to the so-called boulder against which he's propped, he scratches some of the contents onto his finger and tastes it. Suddenly, he ecstatically comes to the conclusion that he has discovered a "carrot mine" and starts to frantically dig through the carrot.
On the other end of the garden, Paul Bunyan leaves his log cabin for work with his dog, Smidgen (a gag in itself, as the word is a measurement for a small amount), following behind. Paul instructs the dog to watch over the garden and literally leaves over the mountains.
Back in the garden, Bugs has managed to tunnel through several carrots and lay down tracks for the mining cart he is using to dump the excess carrot chunks over a cliff. Smidgen, drawn to the sound of Bugs' singing, pulls up the carrot that Bugs is in with his teeth. Bugs comes out, stops at the sight of what he assumes is a large billboard (Smidgen's dog license), and wonders where it came from. Suddenly, he realizes that he is suspended high in the air, and frantically climbs up the carrot onto the edge of Smidgen's nose. Bugs then sees the large bloodshot eyes staring at him and realizes what he's up against. However, he becomes enraged, stating to the audience: "I'll be scared later. Right now, I'm too mad." He climbs up, approaches Smidgen's eye, and balls his fists to fight. Smidgen takes his fingers to flick Bugs off his bridge, but Bugs jumps up causing Smidgen to flick his own eye. Bugs then walks through the dog's head, out the left ear to the ground below, and runs down the garden with Smidgen not far behind.
Bugs then happens upon a wormhole and dives in forcing its previous occupant, a worm, out. Smidgen sticks his nose over the hole and starts to sniff, unbeknownst that Bugs has a feather, which he uses to tickle Smidgen's nose, causing Smidgen to give a hearty sneeze that rockets Bugs into Paul's cabin and inside a moose call horn. Smidgen runs into the cabin, grabs the horn and gives several blows that alert a nearby moose. The normal-sized moose happily runs after what it believes is another moose, only to find in waiting an enormous dog. The moose instantly flees, yelping like a dog. Smidgen gives the horn another blow, sending Bugs flying into the barrel of a revolver. Smidgen fires it, sending the bullet Bugs is riding on into a nearby apple in a fruit basket. Smidgen grabs the apple and takes a large bite, leaving Bugs' lower half exposed. Smidgen then eats the entire apple, grabs a toothpick to pick his teeth, and walks away, assured that Bugs has been eaten and taken care of. When he picks his teeth, Bugs comes out unharmed on the top of the toothpick. Bugs then hops up grabbing Smidgen's ear and wraps it around Smidgen's head covering his eyes. Then Bugs dives into the hair on the back of Smidgen's neck. From there, Bugs proceeds to scratch the surface of Smidgen's skin, distracting the dog long enough to allow Bugs to exit via Smidgen's leg and leave the cabin. Smidgen chases after Bugs, except now he wants the rabbit to continue scratching. Bugs, feeling as though he's safe, stops to catch his breath, not knowing Smidgen is right behind him. Before he knows it, Bugs is licked by the dog's enormous tongue, which lifts him off the ground each time. Bugs tries to run away, but stops at the sight of something. Quickly, he sees the world's largest redwood tree and calls Smidgen's attention to it, and the dog runs off to it.
"Lumber-Jack Rabbit" is available on the Looney Tunes Superstars DVD. However, it was cropped to widescreen.
The only concession that Lumber Jack-Rabbit made to the 3-D format was at the very beginning of the cartoon, where the zooming "WB" shield zooms in but at an extremely fast pace (with the shield overshooting its mark and crashing into the screen before pulling back to its correct position). The effect is heightened by a much different zooming sound effect and a banging sound effect before the Looney Tunes theme plays. (This was also recycled into the opening title sequence for The Looney Tunes Show 57 years later, but the shield closer.) This has scared a few amount of people as children. It even scares you if you do expect it.
The closing sequence is modified as well, with the "That's all Folks!" script fading in rather than being written out.