The land in Laṅkā is wooden

Once Kaṡyapa's son Garuḍa expressed his desire to have a hearty meal to become strong enough to save his mother from the snakes. Kaṡyapa told Garuḍa about a huge elephant and a tortoise at the bottom of the ocean and told him to devour them. Garuḍa carried them onto a nearby Kalpavṛkṣa tree to enjoy his meal. But the weight of the well-built Garuḍa, together with the elephant, caused the tree branch to snap. Garuḍa held the branch with his beak stopping it from falling on the Vālakhilya (thumb-sized ṛṣis) who were meditating under the tree. Garuḍa then asked his father what he should do with the broken branch. Kaṡyapa directed him to take it some place far away. Laṅkā was established on this branch of that Kalpavṛkṣa tree, and therefore the land there is wooden.

[1] Tales from the Kathasaritsagara, Arshia Sattar (translator), Penguin Classics, 1994.
[2] The Ocean of Story, C. H. Tawney (translator), C. J. Sawyer Ltd., London, 1924.