In fact it is a tiny islet, no more than fifty feet wide in any direction. It is to be found in a river that flows through dense forests, near the border of the Gillikin and Munchkin Countries. The Magic Isle has one inimical property: living flesh and animal tissue (like shoe leather) takes root on the isle like plants. People who stand upon the island will quickly become rooted to the spot. Wood, however, is immune to this rooting tendency.
The Isle was once the place where a Magic Flower could be found, growing in a golden flower pot. That Flower was removed by Trot and Cap'n Bill as a birthday present for Princess Ozma. (The Magic of Oz)