I wrote the scene with the trees, mountains and beach. The terrain is generated from a height map stored as a greyscale image. It's built out of rows of triangle-strips and colored according to height. Afterwards a procedure generates a few thousand trees of slightly different shapes, heights and color and places them randomly on all parts of the map within a certain height-range.
The sunset background is two quadrilaterals stacked vertically. The six vertices of the background polygon blend together colors sampled from six positions in a digital photo of a real sunset. I ran out of time to figure out texture-mapping so that made for a quick solution that would look good.