The Good Dinosaur was "the first Pixar film without matte painted skies; all 800 shots with visible skies were fully modeled, dressed, lit and volume rendered." Its ridges came from "USGS (United States Geological Survey) satellite data". But on a flat screen a near hill and a far mountain can be the same size, and painted one dark colour they stack like cardboard. Leonardo da Vinci named the fix "Aerial Perspective": "if one is to be five times as distant, make it five times bluer." The air between you and the mountain is lit by the sun; each stretch sends you a little sky and hides a little mountain, so far ridges slide toward the sky's colour. Pixar volume rendered "a planet-sized atmosphere" with a "haze amount" control "to produce consistent atmospheric perspective". On a day you can see 50 km, a dark ridge at 50 km keeps about 2 % of its contrast (our computation). "We're trying to create a believable world," as Pixar's Danielle Feinberg put it.

Our own mountains, sky and computation; no frames from any film.

Which mountain view do you still remember? Tell us where.

Sources: Pixar, The Good Dinosaur SIGGRAPH 2016 talks; Leonardo da Vinci, notebooks (J. P. Richter, 1883); Lord Rayleigh, 1871; WMO Guide to Instruments and Methods of Observation (Koschmieder's law); Danielle Feinberg, TED.
Sounds: our own, made in code (earshot, CC0).