Am I to assume this grave plate is in the ground in a cemetery?
Do you also believe it to be the grave site of your ancestor?
My assumption is that it may have been a foot stone for your man, signifying
his service in the Union Army for the period 1861-1865.
GAR stands for the organization of Union Veterans of the Civil War.
VA tombstones/monuments, may be obtained, providing he is buried without a proper marker existing.
George Martin