If you can't read this, the gist is that the cairns were probably built by farmers in the 18th and 19th centuries for field clearing and storage of rocks for later use in construction or for sale. It does raise the point that there is no written record of cairn building by farmers. One would think that such a laborious chore would have been mentioned in diaries or farm ledgers, and that cairns would have been depicted in American Primitive paintings of farm landscapes. This cairn field also has a large platform cairn.
Why would a farmer go to the trouble of lifting the rocks onto a boulder instead of piling them on the ground? I am skeptical for the following reasons. If this site was a farm quarry, it would have been a great deal of labor to carry the rocks downhill to build cairns. Every other quarry I've seen had large piles of rock close by. The interpretive sign suggests that the cairns were built as part of field-clearing. If the farmer was going to plow the field, he would not have left cairns in the way, and since he owned horses, he could have removed the rocks in a stone boat. Finally, cairns are often found in swamps and on hill tops, odd locations for field clearing.
I might suggest two origins for cairns. Since they are often near propped boulders or openings in the earth, they may have had some Native American ceremonial function. Addition of quartz to cairns also suggests spiritual significance.
Cairn building may also have been a Native American field clearing practice. For workers using only hand tools, the easiest way to get the rocks out of the way would be to put them in small, regular piles. This also may be why platform cairns are so common, as an effort to get the rocks off the soil. Then the native women could have planted their crops between the cairns. Use of cairns as native field clearing may also explain why cairns are often found at abandoned farms. The farmers obtained cleared fields from the Native Americans, and left the cairns in place if they did not interfere with farming. At small farms such as the "Hidden Walls" farm (10/20/11), the native farmer may have built cairns to clear his rocky fields. That would explain why this small farm is surrounded by cairn fields (red dots)