Recent (?) Prayer Seat

Came upon this in the hill/valley/wet areas east of the entrance to High Ridge:

Now look at the birch branches covering the pile:

If it is true that the end of the ceremony involves closing of the seat (something consistent with most examples of small 'U's) then it is being done here with birch branches. Since birch decomposes quickly, how old could this prayer seat be? Not that old.
Recall I found one on Snake Hill in Ayer with an iron pipe "closing" it. This indicates widespread use of prayer seats in Massachusetts up to the last -say- twenty years. That is the present.