At first, I just assumed that these giant dinner mints were man-made. They're actually a rare, natural phenomenon known as "snow rollers." According to The Cellar, snow rollers can only form when the ground is covered in a layer of ice (so that the snow won't stick to it), and when the wind blows gently enough to nudge the rolls forward without breaking them. Also, the snow itself has to be "wet and loose, with a temperature near the melting point of ice." Having all three conditions occur at the same time is pretty unusual, but supposedly the deliciously minty-looking phenomenon can occur anywhere (meaning anywhere that's snowy and gusty enough). The first photo is from the Idaho panhandle, and the second is from Cincinnati.
Story via the always stunning The Cellar.