This U2 spy plane is a "U-2S" model which means a two seated trainer. It doesn't have to be that they are using it to train, but that is a high likelyhood in this case.
However there was a second U2 plane, "U-2A" One-seated general use plane the same time which headed up past Reno and then more north before I stopped tracking it yesterday.
Something to not about these panes: This is not what you just send up willy-nilly if you get the feels for it. They have special fuel to cope with the altitude, the pilot must breathe pure oxygen for an hour before taking off, transport to plane with portable oxygen supply. Also, they are a heavy workout to fly which means difficult and unstable so you have to compensate all the time.