In reply to MikeLell:
Could it also be that they were formed from volcanic plugs that intruded up to a point where a impenetrable stratum in the country rock that effectively capped the intrusion, or at least made it branch sideways into dykes that have since been eroded away. The peaks look too cleanly horizontal to have been eroded to me.
I should warn that this opinion is based on absoutely nothing but 1 semester of geology and a whole lifetime of pulling random ideas out of my posterior.