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with all the sophisticated sonar and underwater maps.  how did they run into a mountain? 
The sonar is definitely sophisticated, but passive sonar isn't too good at hearing what doesn't make noise, and generally speaking an underwater mountain doesn't make any.  I know that the really technical will point out that if you were in front of an obstacle that size, the simple fact that the sound return from that area would be different would tell that something solid was there.  
OK, true. But at 35+ knots? 
As far as the active sonar is concerned, sure you could use that to find out there's an inanimate object in front of you. But submarines don't use active sonar to navigate for the same reason that in combat you wouldn't use your tank searchlight to help avoid obstacles if you were trying to sneak across a field to approach an enemy position.  (See also Murphy's rules of Combat #25, i.e. "Tracers work both ways")
You have to rely on charts.
As far as those are concerned, my son tells me that some of the data being used for certain areas of the Pacific goes back to WW II and some of it even further. That's a HUGE area, and not only is it difficult to get all of it mapped perfectly, it isn't static either. 
I understand that NIMA MAY have had some better data that the boat didn't have.  Whether that's true, and whether it actually shows the obstacle they hit, and whether that could have prevented the collision will probably be part of the board proceedings.
If the skipper was where he was supposed to be, doing what he was supposed to be doing, the way he was supposed to be doing it, and had NO ability to predict or avoid the obstacle, he should be held blameless. But he probaby won't be which is a damn shame given what happened afterwards. 
And even if they don't hold him responsible, the only PRACTICAL effect is likely to be the avoidance of any criminal charges under the UCMJ.
It's sad, but that's just the way command works.
Tom