A few hundred yards from the "outcrop" site in Groton, which I reported yesterday, was this small U-shaped structure - which I think of as being a prayer seat. My speculation about ceremony is that a ceremony should have a beginning, a middle, and an end. At the beginning materials would need to be collected and certain tasks performed. In the middle the details of the ceremony take place and, at the end, the site must be finalized and the ritual items formally "de-commissioned". For prayer seats this seems to mean "corking" or blocking off the space created by it. In this example, there is an iron pipe stuck in the ground acting as a blocking off of the prayer seat.
Here is the view out the "U". This is not directed towards the outcrop , leading me to think it is un-related to that site.A little left of the central axis and about six feet in front of the "U" there is a small green object on the ground. On closer inspection we see an old enameled pot.
The age of these artifacts might be determined. For me they do not seem to be more than 50-100 years old. I assume these are contemporary or slightly more recent than the outcrop site. So again we see this theme of Native American ceremony taking place in this century.