Amchitka Island was chosen for this testing because of it's close proximity to Russia.  The US State Dept wanted to bring the Russians to the nuclear arms race bargaining table so it was reasoned that detonating the largest bomb we had close to Russia would get their attention.  Soon after, the SALT 2 (strategic arms limitation treaty) was signed.   Amchitka Island, in addition to many of the Aleutian Islands, had several generations of US military activity, which are still present in some form.  WW2 bunkers, plane pieces, and crumbling structures litter many of the Islands.  Unused air strips are everywhere and I think that Amchitka's is like 8,000 feet long.  The Cold War's "over the horizon  radar" ground antenna on Amchitka is 3 miles long and was still there back in the late 80's when we prospected the area for new halibut fishing grounds.  I'll never forget the large flat fish that we caught about 25 miles NW of ground zero.  A soft ball sized tumor in her gut cavity!