There's another X to the South, and they both look like they were cut and filled to level the grade. The southern arms appear to be cut and the northern arms appear to be fill.
"Incidentally, on either side of the town of Thurso, you can find the sites of two former US Naval Communications Stations (NAVCOMMSTA) at Forss (beyond the country hotel at Bridge of Forss) and at West Murkle, on top of Clardon Hill.
From the 1960s and 1970s, the sites provided key command and control signals for warships patrolling the North East Atlantic. They were only closed in the 1990s when the communications systems were changed. The old Forss base is being turned into a Business and Technology Park and also houses a wind energy farm (further below)."
Former antenna mast sites?
There's a secure compound to the west too.
"Incidentally, on either side of the town of Thurso, you can find the sites of two former US Naval Communications Stations (NAVCOMMSTA) at Forss (beyond the country hotel at Bridge of Forss) and at West Murkle, on top of Clardon Hill.
From the 1960s and 1970s, the sites provided key command and control signals for warships patrolling the North East Atlantic. They were only closed in the 1990s when the communications systems were changed. The old Forss base is being turned into a Business and Technology Park and also houses a wind energy farm (further below)."
From some nutty Englishman's site: http://homepage.ntlworld.com/alan-turnbull/secret3.htm