Pardon me, but since nobody else has stepped forward to correct the mis-identification, I must do so. E.C. Mason's find is definitely not a "US Army cap-badge. It is a US Army "Geat Seal of the US" horse-harness rosette, in service from 1902 to the present day. This specimen's brass attachment-bar is broken off the rosette's back. If you rotate the photo of E.C. Mason's find, you'll see the "stubs" match up with the location of the crossbar's legs in the photo below. I'll include a photo showing it on the horse bridle. By the way, it wasn't used just for Cavalry... any kind of US Officer's horse also had it.