Vertical silos are still in use by farms that have them, but if they need to expand their storage, they are likely to build a "bunker silo," a flat concrete bin that can be topped with a heavy-duty plastic tarp, from which silage can be removed from the side with a loader as needed. On this picture, taken on a day later in the season while rain clouds were advancing from the east over the Green Mountains, Foster Brothers Farm in Middlebury was packing down chopped corn before covering it and letting it ferment. This packing job is typically done by driving a tractor back and forth over the heaped silage, a job that can be dangerous if the slope is steep enough for the tractor to tip over.