It seems to be - as the Pentagon announced - just a test of an unarmed Trident II SLBM, which makes sense because there was a military exercise going on yesterday in the Pacific Ocean near California, diverting air traffic away from the area. You can also see what looks like separation of the first stage of the missile in some of the videos online.
These missiles are capable of carrying a thermonuclear payload, and usually these test fires are nothing to worry about, especially since I'm sure we conduct them routinely. Although, this one does seem somewhat ominous, given the tensions going on lately between the U.S. and Russia / China.
