This is from 1998:
I went back this afternoon to Wetherbee Avenue, in Acton Conservation land, to try to find some "mounds" I had seen earlier. I did locate one, and also got a photo of the first field clearing pile that I measured. Here it is, the classic field clearing pile. You can see my blue chalk marks for the quadrant I measured. This pile could be mistaken for a turtle mound because of the large "head" to the left. However there are several other large rocks of this size underneath this one and to the left, so it is not a solitary large rock. There are other characteristics that distinguish this as a field clearing pile. Firstly it is a recent pile, there is little buildup of debris and the rocks are still pale. Secondly all rock sizes (except six inches) are well represented, with many more of size six inches. Thirdly the pile is uneven, with many rocks strewn around the edges as is expected since a field clearing pile does not need to be well made. Apparently one key characteristic is the presence of small rocks. There are many six inches and smaller. This is not at all the case for the other piles measured today, where a six inch rock is rare and most rocks are between eight and twelve inches. Forthly this pile is at the edge of a field. Another important characteristic of field clearing piles is the slope of the rocks on the surface. This is called the "angle of repose" which is the natural slope assumed by material piled up and allowed to come to rest under the force of gravity. Roughly this is the same angle as you see in the banks beside the highway, and it is visible in the classic field clearing pile. Other piles examined are either low, without height or are domed, indicating careful construction.