It looks like something man-made, but Mike Stanford, the man who spotted, and photographed, this oddity claims it is a natural occurence, though only under the rarest of conditions.
From the Seattle Times :
..snow rollers (as they're also called) form when there is a hard layer on the snow, covered by several more inches of dense snow.
"Then you add a steep slope and a trigger such as a clump of snow falling out of a tree or off of a rock face."
As gravity pulls a clump down, it usually rolls down the hill and collapses, creating (what is also called) a pinwheel. Or it will not roll at all, and come down in an avalanche of snow. But if the snow is the perfect density and temperature, it rolls down leaving a hole in the center...Strong, gusty winds also can be a factor...