Maybe an aiming point for a transit or some other surveying equipment like Mad_Mat suggested. It is only about 400 yards from the portage to Wickstead and would likely be visible from there with magnification. I wonder if the park people are doing any surveying or mapping.

It would be interesting to know if the runs are from when it was made or if they came after the rain on the evening of the 4th. I may have to go back next year and see if it is still there.

Pat