In the high alpine region, at altitudes of 10,000 to 12,000 feet, sometimes patches of pink or red appear on snow. The phenomenon is commonly seen during the summer months in the Sierra Nevada of California where temperatures remain low enough for snow from winter storms to hang around until summer. Compressing the snow with your boot leaves a distinct footprint the color of watermelon pulp, and the color can stain your boots or pant cuffs. The snow even has a fresh watermelon scent and is therefore commonly called "watermelon snow."

The mysterious snow had puzzled climbers, explorers and naturalists for thousands of years, including the ancient Greek philosopher Aristotle who left the first-known written accounts of watermelon snow. At that time, no explanations were given. Centuries later some people began to speculate that the reddish color was geological in nature, either being caused by mineral deposits on the snow or chemicals leaching from rocks.

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