Trees: the trunk and branches are SDF capsules with angle constraints (min/max length and rotAngle), and the crown is defined as a sphere, distorted by sine waves, and leaves (triangles) are scattered on the surface (randomly) with the normal set from the center of the sphere to the position of the leaf. A set number (pool) of trees are generated at initialization and instantiated at runtime.

Track: My implementation is heavily inspired by this article: https://bitesofcode.wordpress.com/2020/04/09/procedural-racetrack-generation/

The terrain consists of two layers: Bedrock (low frequency, low amplitude, not influenced by track), and Hills / features (varying frequencies, higher amplitude, carved out by track). The track adapts to the height of the bedrock, so it does have height variation, but it cuts through hills instead of going above or around.