BOISE - Thousands of snowballs rolled in a flat central Idaho field look like the work of hundreds of ambitious kids - except there are no human tracks.
A rare weather event caused the spontaneous snowballs at the Nature Conservancy's Silver Creek Preserve and surrounding fields near the tiny town of Picabo.
Preserve manager Sunny Healey spotted the cylindrical shapes up to 18 inches high on Jan. 30 following an overnight windstorm.
She says she had never seen them before but a local rancher told her he's spotted them twice in previous decades.
Jay Breidenbach of the National Weather Service says so-called snow rollers are caused by an unusual combination of a couple of inches of snow with the right water density and temperatures near freezing, followed by strong winds.