Actually, I'm not sure if "The Crystal People" by Jack Snow, first printed in the Autumn 1967 issue of The Baum Bugle, quite counts as a short story, as it appears to be a chapter from an earlier version of The Shaggy Man of Oz with an added subplot about Cap'n Bill leading a sailing expedition to find the headwaters of the Gillikin River. (I suspect this is from an earlier draft of the novel, as the Shaggy Man is on the boat, whereas in the published book he was off having adventures with Twink and Tom outside of Oz.) The expedition sails into a cavern with pillars of crystal growing from both the ceiling and the ground. It turns out that these crystals are people: Men growing from the ceiling, and women rising up from the ground. Prince Stalag tells them that they are all looking forward to the day when they will grow together and join up, and then they can leave the cavern and take their rightful places as the true rulers of Oz. This concerns Ozma, who is part of the expedition—until Stalag tells her that that day is over 340,000,000 years in the future. Ozma decides she doesn't have to worry about it much, and the expedition moves on.
The encounter makes for an intriguing event on its own, but I'm glad it never got published in a book. It would have been one of those one-and-done adventures that doesn't add anything to the story or the characters. If Shaggy Man was running long, I can see why Snow's editor suggested cutting it out.