What are these diagonal marks on my innertube?
Those are scuff marks from running the tire flat (or nearly so), and/or from a tire whose sidewall is breaking down.  

One suspects that underinflation played a significant role in this tire failure. If you can see "ripples" in the side of the tire while you ride it, it's way under-inflated.  One wall of the tire will tend to fail before the other, based on the rotation and the diagonal cord alignment. The spacing corresponds to where the tire rippled as you rode it -- it repeats in the same location on each rotation since the sidewall gets softer and softer there.