This is one of those places that makes you go hmmm.
It appears to be something of a conscious design that has fallen into ruin over time, nothing that would imply a shelter of any sort and I wouldn’t use the word “altar”.
Possibly a totem of some kind but I’d hesitate to attempt to affix a date to it – could be relatively new or it could be old.
Lot of wild turkeys in the area and a small stream or rivulet depending on the time of year and amount of runoff or rainfall.
I’ve got some other photos of it from it various angles and the surrounding area but need to root around to find them.