Black and white view of a tractor hauling wood.
Caption: A steam driven snow tractor hauling wood to a dredging site for use in thawing frozen gravel in front of a dredge. Below a foot or so, the ground was always frozen - except in gravel stream beds - "perma frost". As much as 10,000 cords of wood would be accumulated for these operations. (About this time cold water thawing was developed - wood had become too scarce and expensive.)