POSSIBLE MOA INCURSION. FLC IS CONCERNED ABOUT FLYING INTO MOA BUT THEY ARE UNDER ARTCC CONTROL AT ALL TIMES. ARTCC GIVE VECTORS AROUND THE MOA AREA.

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SACRAMENTO (SAC) TO THUNDER BAY (YOT) NAVIGATING BY FMC'S UPDATED BY VOR/DME AND SUPPORTED BY IRS. WE CHKED IN WITH ZLC ATC IN THE VICINITY OF BATTLE MOUNTAIN (BAM) AND AFTER INITIAL CONTACT WE REQUESTED CLRNC FMC NAV DIRECT TO THUNDER BAY. AFTER A SHORT TIME WE RECEIVED OUR REQUESTED CLRNC AND PROCEEDED DIRECT TO THUNDER BAY. APCHING THE VICINITY OF SHERIDAN (SHR) WY STILL UNDER THE CTL OF ZLC; BUT TO A DIFFERENT CTLR; WE WERE SUDDENLY GIVEN A 40 DEG L TURN OFF COURSE; SHORTLY TO BE FOLLOWED BY 2 MORE L TURNS UNTIL WE WERE HDG ABOUT 100 DEGS L OF OUR ORIGINAL ON COURSE HDG. WE INQUIRED AS TO THE REASON FOR THE TURNS AND WERE INFORMED THAT WE WERE ABOUT TO ENTER AN ACTIVE MOA (MILITARY OPERATING AREA) AND HAD TO BE VECTORED AROUND IT. IT WAS FURTHER EXPLAINED THAT THE MOA WAS NORMALLY ONLY ACTIVE FROM FL270 AND BELOW; BUT TODAY WAS ACTIVE FROM FL400 AND BELOW. THE VECTOR OFF COURSE LASTED 21 MINS BEFORE WE WERE RECLRED DIRECT TO THUNDER BAY. THIS WAS RATHER DISCONCERTING EVENT. WE WERE CLRED INITIALLY INTO AN ACTIVE MOA THAT NO ONE APPEARED AWARE OF UNTIL THE LAST MIN. WE HAD NO NOTAMS OR WARNINGS OF THIS AREA; AND THERE WAS NOTHING SHOWN ON OUR CHARTS OF SUCH AN AREA.