Redwood City seems to be spot on.
For what it's worth, I tried to further narrow down the datacenter locations with some latency measurements, since Amazon seems to be pretty secretive about precise datacenter locations within a certain region.
West Coast: between SF and Santa Clara (
@Lord Frodo Do you know the precise locations of the us-west-1 datacenters?
)
East Coast & Login: Ashburn, VA (us-east-1, "closer than 1ms")
Europe: Dublin area (Ireland, eu-west-1)