As the days grow shorter, so do they grow colder in the mountains. By the arrival of winter, snow begins to fall. What starts out as a few inches in only the highest elevations, ends with enough snow to burry a forest. It's a gradual process, as with everything that shapes mountains. Whether it's glaciers sculpting granite or simply the slow accumulation of a winter's snow, with enough time, the landscape changes. Mountains are a continual work in progress. These photos show how winter transforms the Sierra.