This article is from the Fractal FAQ, by Ermel Stepp email@example.com with numerous contributions by others.
Usually by a method such as taking a triangle, dividing it into 3
subtriangles, and perturbing the center point. This process is then repeated
on the subtriangles. This results in a 2-d table of heights, which can then
be rendered as a 3-d image. One reference is:
1. M. Ausloos, _Proc. R. Soc. Lond. A_ 400 (1985), pp. 331-350.