The odds against a stone being naturally upright are very slender indeed and the problem with upright stones is in determining when they were actually placed upright. There are huge areas of undiscovered prehistoric remains that have been unresearched because of any number of chance events. Bringing unknown monuments to light is a dangerous occupation - there is no assistance from anywhere and nobody is at all interested in what you've found - unless it's oil, gold reserves or deceased poultry.