The Forbidden Mine (Part One):
Gumby has a surprise for Minga, Prickle, Goo, and Pokey: a picnic at the very edge of the Grand Canyon. Afterward, they decide to explore an old mine. The mine's caretaker isn't pleased with the idea, but for no reason at all he warms up to them and lets them in. They go 2000 feet down to take the grand tour of the hole in the ground. Unfortunately, there's an earthquake and subsequent cave-in, trapping Minga behind feet of solid rock!
Gumby and friends are sick of being a farm and band and decide to get some robots to take over the farm so they can concentrate more on the band. While they're away, Tillie admires herself in Gumby's computer monitor, walking all over his keyboard in the process. The robots, naturally, go haywire. Fortunately, Denali calls Gumbo to come over and take care of them while Gumby and friends make their way back from a concert.
The Forbidden Mine (Part Two):
Gumby and Prickle move the rocks out of the way, only to find that the mine is flooding and the elevator doesn't work! It's up to Goo to fly to the surface and get some help. She finds Gumbo, who gets Denali and two thousand feet of rope, and hauls everyone safely to the surface. Minga brings back a giant, solid-gold nugget as a souvenir.